Make sure you get some protein also. Survival food is deliberately low in protein, because it takes a lot of water to digest/metabolize. That's what you want in a survival situation, but not losing weight.
The make a special version of Mainstay with protein, but you have to have water with it...They sell it for relief operations in which children may have to live off of the stuff for a while, but not for survival or the first week or so of a disaster.