Rice. Rice is a staple part of our diet over here (and they always make too much - I should talk to Jenn and 'dul about that). We have chicken and rice; beans and rice; chicken, beans, and rice; fish and rice; fish, beans, and rice; rice and rice; rice, rice, beans, and rice; chicken, rice, beans, rice, rice, and rice... you get my drift. And if we had spam, I'm sure it'd find its way into my litany somehow :)

Beans - canned or dried. Dried beans are a heck of a lot cheaper, but you *do* need to plan to use them.

My sister always has a ton of canned tomatoes, and they find their way into most things - pasta sauce (really easy to make, and I bet you didn't know that), beans, whatever.

Potatoes. They're not the most healthful of root veggies, but they keep, and they can be added to anything to bulk it out. Sweet potatoes are better for your health, but they take longer to cook, I find.

Onions and garlic. EVERYTHING ultimately is improved with onions and garlic.

I'll think on it some more, if you like. You'll note I'm only listing things that keep. Things that get used up, unless you love them, you don't really want to just keep on hand. Buy them as you need them, and only as much as you'll use, you know that.