I think they come in several types depending on re-supply options. I grew up in a military family, ration packs would be a staple of family camping holidays! The 24 hour survival pack would feed a kid for a long weekend, it's intended to keep an active soldier healthy and hydrated, that last point being key if considering using them for anything else. The meals are ready to eat, heating optional, and also contain enough fluid for survival, therefore they're not light, if you have access to water anything dehydrated would be better. I think there are such military packs, but there's also a whole lot more choice, specialist stuff from adventure suppliers or even the supermarket. I usually carry at least one such supermarket meal as a back up, flavoured couscous or noodles.
