Oatmeal

I eat it almost every day. Helps keep up my milk supply, is cheap (especially in 25 pound bags from the church), and tastes so, so, so good when done right. Here's my routine:

one part regular oatmeal (not quick, not instant, just oatmeal)
one and a half parts milk

Microwave for three or four minutes. I add brown sugar; add cinnamon too if you want to feel like you're having rice pudding for breakfast. Or fruit, or shredded coconut, or anything else delectable.

Here's what you don't want to do: buy oatmeal at McDonald's. Just don't. If that isn't intuitive for you, check out Mark Bittman's recent piece. Blech. Nothing worse that fast, cheap, healthy food turned into something vile and not really food at all.