For most of us when we are honest with ourselves, we ask questions like, "Do I really need all this stuff?" Especially for those of us that live in the western cultures of capitalism and consumerism, the brutally honest answer to that question is a resounding, "NO!" Unfortunately this answer is not very popular, either with ourselves, or with others around us, as we are all chasing each other and trying to keep up with those proverbial Jones' (BTW I still haven't caught them yet).
"Capitalism is probably the most formative structural reality within our society. It sets the course for most of our lives, shaping what we considered to be worth having an giving us a context in which to pursue those things. Certainly for most in the Western world, capitalism has become the taken-for-granted shape of things, as permanent and unquestioned as the sealed roads and powerlines outside our houses." (Jonathan Grant - Divine Sex)
Our capitalistic culture is so pervasive that it gives us what James K. A. Smith calls "secular liturgies" - "the visions of what life is all about: what will bring us satisfaction, what will save us, what will give our lives meaning and significance, what will add up to the good life. Smith warns that we can avoid overtly religious liturgies by not attending church, but we cannot avoid cultural ones. They are all around us, and they seek to capture our imaginations, to tap into our deepest desires, and direct our worship toward rival gods."
Here are some helpful ideas that I have wrestled with employing in my own life in order to downsize and fight against the trappings of this world and it's constant barrage of telling me I need more stuff (here is an interesting article discussing the barrage of the 5000+ ad and brand message the average person encounters per day).
Go Through Your Closet
At least once per year go through your closet thoroughly and get rid of everything you haven't worn in the past year and give it away (I know this can be very difficult for some of my fashionista's out there, but don't kid yourself, if you didn't wear it last year, it's not likely you will wear it next year)
Buy Used
This tactic not only applies to automobiles (which if you buy new, dramatically depreciate in value once you drive them off the lot) but also for more common items like clothes, furniture, electronics, etc. I have found that the more I buy used, not only do I save on the initial sticker price, but also the less I tend to covet it and the less I care if it gets 'gently' worn after purchasing it (thus helping the dynamic around my household).
Challenge Yourself
Find something really difficult for you to part with, and challenge yourself to get rid of it. For me I really liked watches (hey it's the only socially acceptable jewelry allowed for men!) so I challenged myself that anytime someone commented on how much they liked my watch I would give it to them off my wrist (of course I can't do this forever unless I continually buy watches, which of course would defeat the purpose).