I'd like to quote my man, HD Thoreau: "A man is rich in proportion to the number of things he can afford to let alone."
Personally, it has taken me about 3 years to rid myself of nearly everything I own-- it isn't as easy as they'd think. Right now, everything that I own can fit in my 40L REI backpack:
I own: 7 t-shirts and 2 button down shirts, 1 pair of jeans, two pairs of khakis, and 1 pair of corduroys, 7 pairs of underwear, 7 pairs of socks, one pair of Converse and one pair Clark's desert boots; a netbook, cellphone, camera, a notebook and pen, sunglasses, some books, and a watch. I do have my dad's bike, his Bose speakers, and his receiver at my current apartment, but those hardly count. I live in an apartment with 4 friends, and I pay $150 a month in rent, allowing me to make a profit of $1600 a month as a bartender--easily sustaining my minimalist lifestyle.
As you can see: even if I don't have a lot of stuff by most people's standards, its still a lot of shit.
The reason I live this way is pretty simple: I like to have as much free-time to myself as possible-- for me, working is more like selling my soul. With no need for a bunch of excess stuff, I only have to work 4 days a week at a job that I like (one that also provides me with food, alcohol, and a social life). I'm free to buy a plane ticket to Thailand, tomorrow if I wanted, because I don't have a bunch of crap I'd need to store or sell or protect while I'm gone.