+1 on the dehydrated potatoes, my personal favorite. I throw in some dehydrated vegetables and bacon bits or beef jerky sometimes. Find a local health food store with a bulk foods aisle, and buy these ingredients that way to save money (only buy what you need for each trip). PineMartyn's advice is sound. But if you can't dehydrate your own or don't want to, this is the way to go.
Another good bet is dehydrated black beans, which are very nutritious and can also be mixed with other stuff to your liking.