I lived in a cabin in the woods for awhile once, and found the aforementioned (brown) rice and beans to be the most useful staples. Millet is good, too, but to my taste, it needs the addition of vegetables, or a bit of meat or fish and some seasonings to make it really tasty. Oats are good to keep around, too, and oat bran, which is now pretty widely available in bulk, cooks up very quickly and doesn’t have to be used as a sweetened cereal. I kind of prefer it with just butter and salt, maybe some Goya Adobo if you can find it.
Often rice and beans are satisfying, to me, plain with just some butter or oil. But to spice things up a bit you can get a masala (such as garam masala) from an Indian grocery; or you can do what I did, and make up a masala of your own. I ended up with a twenty-three spice mix, but that was just me being crazy. You can start with the basics, such as paprika, turmeric, cayenne, chili powder, cumin, white pepper, fennel seed, and so on, mixed to taste, and go on from there. I used to add it to the water when cooking rice. A mix of spices like this can be produced pretty cheaply from the bulk section of a good co-op or health food store, and it will last a year or more if tightly covered.
Ghee, the clarified butter used extensively in Indian and Middle Eastern cooking, is easily made once you get the hang of it. There are a number of recipes available online. It gives you the flavor of butter without the sensitive storage issues – a jar of ghee will keep at room temperature for several months, or up to a year in the refigerator. And, because it’s been clarified, leaving pure butterfat, you can actually fry in it. I used to make it quite cheaply by using whatever unsalted supermarket butter was on sale; now, because I don’t like the idea of bovine growth hormones, I use organic butter.
There are a few Chinese and Japanese items that keep for a long while and can add interest and nutrition to plain dishes, like the Japanese katsuobushi, dried shaved fish flakes, furikake, a seaweed-based salt condiment, and black sesame seeds. And seaweed itself is a good source of extra nutrition. All of these can be stored quite awhile and are available fairly cheaply at Asian supermarkets.