Pasta, and jars of pasta sauce. Canned tuna. Peanut butter and jelly. But mostly what I try to do is freeze leftovers. Any time I make soup (or stew/chili/etc - anything that's easy to do in large quantities), I freeze individual servings to be eaten later.

Incidentally, if you're freezing in plastic bags and if your freezer is large enough to accomodate this, I find that it helps to lay the bags down on something flat (like a cookie sheet) until they freeze. They take up less space that way.