seriously?

why do i have so much stuff? why? it doesn't seem like i should, since everything i own fits into the five categories of clothes, books, movies/music, art and kitchen stuff, but holy crap does it all add up. i'm trying to be really good about getting rid of things i don't use often, but i've got a little bit of 'but i could sell that for money, i can't just throw it out or give it away!' resistance going on. does anyone know a place that will sell stuff for me? i've got a bunch of vintage clothing and quite a few movies, and i don't have the time or the energy to list them myself.