First off: get your mind outta the gutter; not that the truth is any more pleasant than what you were undoubtedly thinking, or anything. Still. I'll wait.
Now then. Butt-hunting is a sign of the truly depraved nicotine addict. If you're out of smokes and broke (or worse, out of smokes and extremely lazy) the only way to satisfy that fix is to relight your filters. Ok, it's not the only way, but it's the easiest and requires absolutely no skill unlike, say, rolling a cigarette out of your tobacco leavings or putting on shoes and making your way out into the world.
Most people don't smoke cigarettes all the way down to their filters, leaving a puff or two of tobacco at the ends. If you've got an ashtray lying around you've probably got a handful of usable butts. Just light 'em, puff 'em and stub 'em, over and over until you feel better. You won't, trust me, but it'll seem like a good idea at the time.
There are all sorts of reasons not to do this - it's embarrassing as all hell, it leaves your fingers reeking of stale tobacco (worse than normal) and it makes you cough a lot more than usual - by the time you've gotten around to these butts the filters have degraded to nonexistence. You're probably better off scrounging around under the couch cushions for change or borrowing some cash from a friend or (heaven forbid) getting around to that whole quitting thing you were thinking about.
More so than anything else, butt-hunting is what divides the smokers from the less cool, much more healthy smokers who always seem to carry tennis rackets and water bottles with them wherever they go.