I spent 29 years as an Army infantryman with the first 7-8 year s spent eating C-Rats. Some of my earliest tactical training memories are of stripping out the C-Rat stuff you weren't going to use and stacking the cans in a tightly tied off spare sock during you pre-combat checks so that they wouldn't rattle and get you "shot".
We knew the beef and potato slices as "beef and shrapnel slices".... And the ham and Lima beans were "ham and mother........"
C-Rats and early MREs didn't come with heaters and getting the solid fuel "heat tabs" fuel tablets was usually reserved for really cold weather so there were a lot of different methods used to heat C-Rats especially. Including puncturing the can and putting it in the empty box and then lighting the box on fire, Sterno stoves, early backpacking stoves, C-Rat cans with a bit of gas mixed in dry sand as a stove and twig fires. And since boiling water wouldn't get hot enough to burst the can just putting all the cans that needed heating into a pot and heating them in water was sometimes an option, too.
Actually, we used to hunt for and trade for the early MRE freeze dried beef or pork patties as especially when added to ramen noodles or dried potato flakes they could be made into a lot of pretty nice meals if you had a few minutes and had done a wee bit of prior planning.
Aside from cost, the big reason they did away with the freeze dried meats and fruits was because despite frequent warnings there were always knuckleheads eating them dry and not drinking enough water resulting in really painful "belly bombs".
I still have several of each size of P-38s and still carry one occasionally. For years after my retirement I still wore my dog tags with one sporting a rubber silencer to keep them from clinking along with a P-38 and a handcuff key all kept quiet with a fat rubber band. I still wear one red dog tag for medical alert purposes but no longer have the key or P-38 on it.