Mountain House was what we usually used for camping. Usually pretty tasty, though not always cheap. Available in pretty much any outdoor store,
and it shows up in a lot of the Army Surplus types of stores around here as well. Lots of variety available from MH as long as the store has bothered to get a wide selection.
For field work, I usually had some version of a civilian MRE, or even the real thing when I had friends in active service. Not always the most tasty, but they'll keep you going.
Some of the newer versions are sold through Ameriqual, MREStar, Sopako, and Eversafe. I've only tried Eversafe so far. Not bad beef stew. Oh, and self heating packs are a wonderful convenience, but follow the directions. Friend of mine didn't, and ended up with improperly cooked stew and a slight burn.
Home grown or farmer's market fare dried in a dehydrator and vacuum sealed gives you a bit more flexibility, but takes more planning up front.
Have fun!
Cheers-
Chris