Be ready for some constipation. You know why there is such a tiny roll of TP in an MRE? You know why there is that funny chemical smell when you first open them? Because there are chemicals in them that tend to bind up a fighting man (or woman's) intestinal tract. It bad enough to be shot at or shelled or bombed. It's worse while doing the Aztec Two-step. MRE's reduce that likelihood. It may mean you don't go for a day or two.