Ditto on everything MiniMe listed, though I like more fruit in my GORP mix, to each his own.

Since they've started selling Tuna in those foil packs, that with some pita breat has become one of my favorite no cook meals. Peanut butter's always good too.

I also like Ramen Noodles, not everyone does, but they're light, easy, and about the cheapest thing you can find.

Hope this helps,
Chris.