I don't really anymore, but I used to be an avid dumpster diver. So avid, infact, I own this shirt:
I used to live behind a strip of grocery stores, Chipotle's, etc. There would be loads of slightly bruised fruit, halves of burritos, etc. There are a few things I think are totally essential when dumpstering for food:
only dive when it's cool (early morning or evening). once it gets hot, the food spoils.
when in doubt, throw it out.
wear clothes you don't mind getting dirty, and shoes that are safe. getting some sort of infection from cutting yourself through your shoes or whatever, totally sucks.
be wary -- some grocery stores dump bleach over all their unused fruit and shit, just to keep divers away. fuckers.
know that
no one can legally tell you to fuck off. as of 1988 the supreme court ruled that trash does not belong to anyone, so it cannot be considered theft. so tell anyone who bothers you to fuck off. now if it's on private property, you're screwed. but most people are so shocked that anyone knows anything about court cases involving diving that they usually back off.