sleep, read, watch tv, masterbate, surf the web, eat, go for a walk, drive around, etc... The best way to stay occupied is to learn a new hobby, I'm fascinated with learning new things: gardening, making beer, learning how the body works, how the universe works!!! Girls are also a good way to kill time but usually cost money on the up side if you're nice to them they'll usually let you have sex with them, I think the ROI is kinda crappy though
I have to stay occupied if I got bored for more than a day or two I get severely depressed