I have a friend who frequently dumpster dives, and while he doesn't find anything regularly, he does find some worthwhile things.
He's found a working PS2 + Controller, about a dozen XBOX/360 games, a collection of baseball cards, all of which he pawned for a decent amount of money. He'll take anything he can't use or sell and scrap it, and he makes... some money from that. Not enough that I would consider doing it, but you'd be surprised what people throw away.
As for food and such, if it's still good to eat (75% of food thrown away from grocery stores), I don't see any problem with doing it. Just be careful, even though they have thrown it away, you can be charged with theft if you get caught.