Like Am_Fear_Liath_Mor said, you can make up your own shelf-stable food supply from less expensive grocery store items.

The advantage of Datrex, Mayday, and Mainstay (haven't tried that brand) is very long shelf life, and their claim to not induce thirst when consumed.

Wasa flatbread, natural peanut butter, jerky, aseptic packed tuna or salmon, dried raisins or currants make good choices.

Any meal or snack is more filling and nutritionally complete if it contains complex carbs, good fat, and protein.