Clothes, among other items. The Salvation Army thrift store around the corner from my place in Clovis had stereo equipment, TVs, couches, records, etc. I bought a T-shirt from there that says, "I spent my birthday at Table Mountain Casino." I wore it to class one day and some girl asked me how my party was up there. I told her I've never been to that casino; I bought the shirt at the Salvation Army Thrift Store for a buck.
Personally, I would never buy underwear from there, but shirts, pants, jackets, etc. are fair game. Just make sure to wash them before wearing them.