As I teach in my Time Management workshops, living frugally is a fundamental success skill. Frugality increases the odds of your getting to live your mission, while spendthriftness increases the odds that you will live beyond your means, go into debt, and never escape from the consumerist treadmill.
Frugal people create options and freedoms for themselves. They don't have to take the job with the long commute, or stay in the one with the abusive boss, just because it pays more. And they can often afford to work part-time or take a sabbatical so that they can work on their artistic, activist, family or other goals.
Frugality isn't the same as deprivation. If there's something that's really necessary for your happiness, work to buy it (as cheaply as possible, and used if possible). But if you're just buying stuff because you think you should, or don't know how else to spend your time, then do some mission work - preferably with the help of a mentor, coach or therapist or other advisor. Remember: frugality feels good, at least once you get past the addictive element in spending, while deprivation feels bad.
A great book to read about frugality is The Millionaire Next Door, which tells how people of ordinary means can live comfortable, even luxurious lives, mainly through being frugal.
Frugality is the rage, now, which is great for us as individuals, our society and the planet. You probably already know about Craig's List, FreeCycle, the Compact and other frugal resources. Here's a fun one I just learned of: a list of thrift stores