I lived on Chinese noodles and sardines for long stretches of time. Toss in a multi-vitamin and you can go a long time on just that. It is a little light on roughage so while your shopping you might want to get a large bottle of generic Metamucil, psyllium fiber, to keep everything working smoothly.

Another limited diet I have used is black bean and rice. Much more balanced nutritionally and it included enough bulk to keep everything moving. But add a large bag of onions, a large bottle of Tabasco to add some variety and a bottle of multi-vitamins to help make up any deficiencies.