What do you usually eat, Ian? I know my food costs are much higher than yours because I get the organic CSA, use olive oil more than before, buy cheese occasionally, make yogurt, and use milk for coffee regularly. And I bake a lot, which means I probably go through butter, flour, etc. much quicker than you do. I don't buy meat very often, though I intend to buy frozen shrimp today for a couple ultra-fancypants meals this week.
I imagine you eat a lot of stir frys, rice dishes, maybe eggs?, and maybe even ramyeon. Potatoes? Enlighten me! :-)
I don't know that I've ever done an inventory of my diet, but now's as good a time as any. To start, my school lunches (at my main school) are pretty good: I always get rice, soup, kimchi, a vegetable dish, 1-2 meat dishes, and periodically fruit or other things outside those categories. This drops my costs and adds variety that I probably can't duplicate in most other jobs.
Cheap Staples:
Rice
Oatmeal
Eggs
Carrots (one of my favorite foods, and I eat a bunch)
Ramen
Seasonal Things: (whichever few are cheapest at a given moment)
Vegetables (tomatoes, cucumbers, more I'm not thinking of right now)
Fruit (apples, pears, persimmons, oranges)
Sundries:
Yogurt (actually pretty cheap, but it's the sugary kind so I limit it for health reasons)
Spaghetti (adding Parmesan cheese knocks this out of the staples rank)
Bread (my biggest luxury expense, though the whole wheat loaves from Tours les Jours aren't terribly expensive)
Dark Chocolate (also luxury, but a little of this completely satisfies many of my desires for less healthy things)
Potatoes (not as cheap as I expected, but I like them and they're still reasonably priced)
Almonds (cheap by the kilo and great snacks)
I don't really like food preparation and it shows. I basically don't buy any meat anymore since I get enough at school and it seems expensive here; I'm a little jealous of everyone who can buy chicken breasts by the pound for cheap - the lowest I've been able to find in my neighborhood is about $5 for a single one (mostly pretty small). Not drinking coffee (never liked it) and not baking (no oven) probably lower my costs too.
I probably forgot about a few things, but that's a reasonably representative list.