Since the days when humans first started walking upright, talking, making tools and wondering what it's all about the nature and scope of human endeavor has changed beyond recognition but the goals underlying our behaviors are fundamentally the same. The precise things that make us happy or which we experience as pleasurable may be very different, but closer examination reveals a set of goals which are probably fundamental to human nature. The influence of evolution on our natures isn't limited to shaping our bodies, it has also shaped our minds and in doing so it has given us a set of intrinsic goals which the reward systems of our brains encourage us to seek. Because food was scarce for much of our evolution we experience eating foods that are dense in energy in the form of fat and sugar as being rewarding and we have a tendency toward laziness (don't waste any of those scarce, precious, calories). These evolved goals persist, even though sweet fatty foods are abundant and most of us get less exercise than is good for us. The above example is fairly clear cut but the evolutionary underpinnings of other behaviors are a good deal more difficult to pin down so I will refrain from taking up too much space presenting what are at best difficult to test hypotheses. The point is, that there is such a thing as human nature, that we have a certain set of drives and needs and most methods for the pursuit of happiness focus on the satisfaction of one or more of these drives and needs.
We need food and water and we desire a variety of food that tastes good.
We need shelter and we desire comfort.
We desire sex with attractive members of the opposite sex (subject to a variety of well known exceptions).
We desire to be members of a group in which we feel that we belong i.e. friendship and a sense of community
Within our groups we desire status and power and we desire status and power for our group over other groups.
We seek to avoid hunger, pain, discomfort and for as long as is reasonably possible, death.
We desire for the world and our lives to make sense and to have control over our lives and our surroundings.
We desire and seek to maintain a sense of self-worth
How happy we are relates not only to where we stand in relation to the satisfaction of our inbuilt goals, but also to whether our circumstances are getting better or worse. The same man could at one moment be miserable because he is living in an uncomfortable mud hut, with a plain looking woman who neither respects nor likes him and who seldom if ever feels like having sex with him, because his food is bland, because he is at the bottom of the village hierarchy and because he has no way of making sense of his circumstances or forming a plan for changing them. Later after spending a half hour of terror being hunted (unsuccessfully) by a tiger, he feels very happy just to be alive, because no matter how bad your circumstances are, no longer being hunted by a tiger is a huge improvement. Or consider how a hamburger could be either utterly mundane and uninteresting or a great treat depending on whether the previous week was spent dining in fine restaurants or being served bread and water in prison.
If improvements in circumstances are associated with happiness, worsening of circumstances (even if things still really aren't that bad) is associated with unhappiness or even outright misery. Imagine how much happiness you might feel if you won a competition that allowed you to have a maid to do your housework for you for year. You would probably be happy at first but after a while you would get used to this privilege and probably not be much happier than you were before. Now imagine how you would feel when the year was over and you had to go back to washing dishes or ironing shirts or doing whatever other chores you dislike. Experience and a wealth of scientific evidence suggests that the loss is felt much more keenly than the original gain even though that which is lost or gained is identical, an effect known as Loss Aversion.
By this point you are probably asking what any of this has to do with consumerism and economic policy. The basic mechanism by which the consumer seeks happiness is by making sure that he or she always has a little bit more than they had before, allowing them not only to reap the psychological rewards of living in a safe and comfortable environment but also those associated with improvements in living conditions, in particular the rewards associated with having more, bigger, faster and shinier stuff. This drive for more is driven not only by the desire for constant improvements in conditions (which we perceive as rewarding) but also by the desire for status. Its not just about having more than you had before, its about having more than the neighbors. This status part of the happiness equation functions just as well at lower average incomes as it does at higher ones, in the poorest villages of Africa the man with the most head of cattle is still happier than the man with the least and more importantly he is likely to be happier than a person at the bottom of the income distribution of a richer society even though his absolute living standard is poorer.
In fact, above a certain level of wealth/standard of living, happiness depends only very weakly on the absolute standard of living, having more to do with the direction of change, status and myriad social factors.
Most of us have a least a passing familiarity with the problems that consumerism, especially when combined with easy access to credit, can cause. You get used to the happy feelings associated with having recently purchased something new, maybe it's a better mobile phone, a bigger car, a better digital camera. When it has been too long since the latest purchase and the happy feeling starts to taper off the temptation to go out and buy something else is like a mild version of what a coke-head must feel when his/her buzz is starting to taper and its time to go in search of the next line or bump.
So long as the coke head has more coke, or the consumer has sufficient income to be able to buy newer and better things all seems to be well. However, if the economy isn't great and the consumer's income stagnates, or other costs (e.g. healthcare) rise, or the neighbors are buying shiny new things at a rate that is hard to keep up with, then the consumer starts to feel unhappy and under pressure. They can respond to this in one of a handful of ways, either by working more hours, by taking on more risk (canceling insurance), by running down their savings or by borrowing money. At first you might try to live within your means, resist the temptation to work more overtime (if you are fortunate enough for it to be voluntary) and spend more time with the kids. But those damn neighbors and their neighbors just got a second mortgage and are working all the hours, they have a BIG shiny new car, they are getting a pool put in and you have a sneaking suspicion they have been getting cosmetic surgery too. You could have dealt with having to tighten the belt a bit if everyone else did it too, but the way things are going your pride can't take having the oldest car and the shabbiest clothes on the block so you pull the trigger and do it.
You work the extra hours or maybe change to a higher-pressure but higher-wage job, you take out a second mortgage to get access to the equity on your home and hope to God that house prices keep rising. You get a newer car, stone worktops in the kitchen, newer clothes and better gadgets and for a while you feel like you are winning. But after a while you notice that you hardly have time for to spend with you wife/husband/children/friends, and most of time you spend in your beautiful house, is spent sleeping. You start to wonder if it is all worth it, but you try to push the thought away because if the way you were living before was hard then, it would be so much harder now to give it all up and go back to how it was. Loss aversion and the need to service your many debts have you trapped in your new high-stress life. Even though you now realize you would happily give up a good deal of wealth and status in order to live at a slower pace and have time for your husband/wife/children/friends and to pursue personal projects be they brewing, political activism, car customization or music, you are in a position which is very hard to get back from and that's even before the bottom drops out of the housing bubble leaving you with mortgage debts bigger than the value of your house. 
If the pursuit of more, bigger, faster and shinier is problematic for individual consumers, it is that much more so at a planetary scale. The problem with this method for the pursuit of happiness is sustainability. Economic growth is derived from one of two things namely efficiency gains i.e. increases in the amount or value of products which can be generated from a given set of inputs (labour and materials/capital) or increases in economic throughput (the amount of materials consumed and wastes produced and the number of man/woman-hours worked). Thus the drive to always have a bit more today than we did yesterday, the drive for growth, leads us to increase the efficiency of our economies but also to increase economic throughput. While it would in principle, be possible to attain economic growth with constant levels of economic throughput (materials and labour in, wastes out) in practice this doesn't happen. The use of labor saving devices which allow one worker to produce more goods and services generally results in increased energy use. This is true for the introduction of tractors in agriculture, jackhammers for digging up the street etc. Indeed these labor-saving innovations also result in the increased use of physical resources, it takes a lot more steel to make a jackhammer and compressor than it does to make a few pickaxe heads. The ultimate problem then, is that at present economic growth is reliant on continuously increasing inputs, and the world is a finite and with respect at least to mass, essentially a closed system. The planet contains a finite amount of the materials on which economic growth relies copper, platinum, rare earth metals etc.
It isn't fashionable these days to point out that the earth's resources are limited. Dire predictions were made in the 1970's about likely food shortages and technology in the form of the green revolution (mechanization, fertilizers and agrochemicals) ensured that the dire predictions were proved dramatically wrong. Instead of worldwide famine, we have an epidemic of obesity and diabetes in the West. Many people remain hungry worldwide, but the problem is one of distribution rather than scale of production.
Historically we have always been able avoid the consequences of shortages either by through technical innovation or through substitution. When wood became scarce in the UK the people didn't freeze to death, they shifted to coal. It is commonly argued that his process of innovation and substitution is self-regulating and that it will allow economic growth to continue indefinitely and any suggestion that maybe we shouldn't be pushing so hard for growth (more, bigger, faster, shinier) is economic heresy. On closer examination this Cornucopian worldview (it'll all be OK don't worry about it and just keep shopping) seems hopelessly naive. While it seems unlikely that we will ever run into an absolute scarcity of some necessary raw material (e.g. copper, it is an element after all and hence in practical terms indestructible) so called Ricardian scarcity is definitely to be expected. That is to say we are being/will be forced to mine ores with progressively lower copper contents in smaller deposits in more remote locations. Now technically this is doable, but even allowing for efficiency gains the likely result is higher costs particularly in the form of energy.
We can deal relatively easily with an increase in the scarcity of one or more raw materials by using more of some other input, especially if this input is energy. With enough energy you could "mine" seawater for almost any metal, it isn't done simply because of the horrendous inefficiency. The real problem arises when a range of material inputs become scarcer at the same time as energy becomes scarce. Oil prices are have been high for a long time and nobody expects them to fall significantly in the foreseeable future. Gas prices are rising. Oil is already being extracted from tar sands despite the punitive energy costs involved and the synthesis of liquid fuels from coal is for the first time being considered in countries not subject to an embargo (south Africa) or a wartime blockade (WW II Germany). On top of all this the carbon dioxide concentration in the atmosphere is higher than it has been for about 3 million years and nobody is quite sure how severe the effects of global warming are likely to be. Even raising the populations of India and china up to the living standards and therefore rates of resource use currently experienced in the west could be more than the planet will stand. To continue to pursue growth as the be all and end all in western societies which have already reached the saturation point on the wealth-happiness curve is foolish in the extreme.
Consumerism and the pursuit of growth as the sole goal of economic policy are costing us in terms of human happiness and putting an unsustainable strain on the planet. A solution to the societal and environmental challenges we face will require us not only to invest in and implement new technologies but also to reconsider our priorities, in short to find other ways to be happy.
It would be daft to expect human nature, after being essentially constant over millennia to suddenly change constantly. People are going to continue wanting status and power and friends and good food and comfort and a sense of purpose. Whatever happens we will still be happiest when things are getting better over time with respect to our inbuilt goals. Humans are tremendously flexible and it is possible to reshape our minds to the extent that we transcend these inbuilt goals, but of those that attempt this very few actually succeed. Thus for most of us it is a question of how we can pursue our inbuilt goals in a way that is environmentally and emotionally sustainable (get happy, stay happy).
The pursuit of status is intrinsic to our nature, it isn't going away, but we need not pursue status by trying to own more and better things than our neighbors. Our drive to compete can be expressed through a number of different outlets; sports, creative pursuits (my homebrew is better than yours...) etc. it is down to us to choose outlets which don't cause us problems in the long run. The flexibility of humanity means that it is entirely possible to imagine a world where conspicuous consumption is frowned upon rather than celebrated, but it will only appear if people decide to lead by example.
Our desire for continuous improvement of one kind or another can again be satisfied through creative pursuits, for example there is no absolute limit on how good a person might get a playing the guitar. A lifetime of improvement and satisfaction is possible without the consumption of significant amounts of additional resources.
In the final analysis the behavior of the economy is nothing more or less than the sum of all the actors in it. As individual actors redefine their priorities, the behavior of the whole system changes. One reason that the growth rate of the French economy has typically been lower than that of the American economy is that French workers/voters have generally decided that they would rather have more holidays and shorter working hours than they would have more money. The problem that we face today is that globalization has reduced the ability of the majority of people to make these kind of choices for themselves.
The balance of power between capital and labor has shifted to the extent that workers often have little choice as to many hours they work or how much annual leave they take. Employment contracts are typically presented in as follows: These are the conditions, take it or leave it. Competition between companies and the obligation to maximize profit for shareholders means that working conditions often vary little between employers in the same sector (pay and working conditions at Burger King are similar to those at McDonalds) and wages for non-managers often stagnate even in the face of record profits. Under these conditions workers seldom have the choice to work less hours and take more leave in order to make more time for other priorities. In the USA at least regardless of whether a job is high powered or minimum wage, annual leave is minimal and long hours are commonly required. For those making just enough to get by the idea of scaling back on economic activity to make time for other things seems like a cruel joke.
For these reasons changing the structure of society in favor of sustainability almost certainly requires a shift in the balance of power between capital and labor and in favor of labor. Of the many different policies which could be implemented to achieve this the removal of barriers to the formation of unions and the taxation of share dividends at a rate similar to that of wages would be a good start. The introduction of these kinds of changes may also require other changes in the structure of society, concentration of media ownership has an innate tendency to distort national policy debate against policies which will empower the majority at the expense of the wealthy. De-mergers in the realms of media and a return of the fairness doctrine could well be a good start. When considering how to vote, consider which party and which policies will empower you the most. Make sure when politicians claim to offer you choices, that the choices on offer are not only open to those with more wealth than you have, or are realistically likely to have in the near future. It is important to look at details rather than the often misleading rhetoric.
At the personal level we should consider carefully before making new purchases and before increasing our expenditures. Debts make us slaves, but savings are power and freedom. While we may fight for a fairer balance between capital and labor, we also need to recognize where the power currently lies and make sure that we each have a least some capital to invest and invest it wisely and ethically. Resist the temptation to move into a bigger place than is necessary, once you get used to the larger house it will cease to be a significant source of happiness, but loss aversion will keep you from going back to old ways and the increased rent/mortgage will limit your ability to save. Learn to recognize quality goods and when you have to buy something new, buy something that will last. Already here living within your means in terms of rent means that you won't be forced by poverty into buying cheap crap which will break and cost you more in the long run, or into buying even relatively small purchases (computers, hi-fi) on credit and thus limiting your freedom and wasting wealth on paying interest to someone else.
In short, think hard about what will really make you happy in the long run, remember that you will get used to any new comfort and it will in turn become a necessity which you have to work to maintain. Better to concentrate on your own development and in the practice of interesting work and pleasurable pastimes that to accumulate things which will bring no more lasting happiness than a child's toys do, two months after Christmas.
