eru nailed it. We lived off bulk everything -- oatmeal, rice, beans. For fresh food, we got cheap veggies with lots of nutrition; greens tend to be the best bang for the buck, but also bags of carrots, beets, and such. For protein, it was all about tofu, eggs, milk, yogurt and nuts (mostly peanuts, soy nuts or pepitas, which are much cheaper than tree nuts). For beverages, bulk tea is absolutely the way to go, at just a few cents per cup.

Food prices have really shot up since 2006 though; in particular, bulk beans have almost doubled. Still, I think it would be possible to eat the same diet today for around $35/week for a couple.