I agree with Xander. Only stuff which gets changed fo' sho' is underwear, but as a guy I have access to a special techinque which allows me to wear the same underwear four days in a row and legitimately claim it to be clean.

Normal
Backwards
Inside-out
Inside-out backwards

Anything else, I wear it either until it LOOKS unclean, or until I get bored of wearing it. Unless, obviously, I do stuff in it which makes it all ew, like go running (Lol).