I've gone dumpster diving on a couple of occasions with some friends of mine. I actually think most people should, at the very least, watch other people dumpster dive at least once. You will be absolutely amazed at the amount of perfectly good food that gets thrown out.

Go to a bakery right after they close. There will be garbage bags full of bread (and nothing but bread so it's relatively sanitary) that was baked that day. Even if you don't eat any, it will probably change your perception of waste.