When I entered the US military, it was transitioning from Meal, Combat, Individual (MCI) to Meal, Ready to Eat (MRE). The former being in cans, the latter in retort pouches. The MCI was the successor to the C-Ration and they were very much alike with both being canned goods. There were times when I was issued a mixture of both; until, the stockpile of MCIs was exhausted.
I never heard anyone call an MCI by that name though, everyone still called them C-Rations. I supposed they felt the "C" might as well imply "Canned" rather than just being an alphabetic type designator. It was much like the situation with "Jerry" cans which derives from jeroboam; but, sounds (i.e. Gerry) like it could be associated with the Germans who were primary users of them.
The canned ration meal was packed in a cardboard box with food accoutrements and accessories. A dozen boxes came in a cardboard case. A few P38s, in individual pouches, were loosely tossed into each case. They neither came in each boxed meal nor were there enough for each meal in the case since they were expected to be reused and those in the case intended as replacements for lost, damaged, or worn out ones.
I would go through the discarded case boxes and scarf up the unclaimed P38s. I left military service with a bag of about 50 of them which I gave away to family and friends. They were novelties to most. Some actually used them for outdoors adventures like camping in which canned goods were still popular. They have a hole in them for wear on a keychain or neck chain (with dog tags). While they were small and light, they had one major drawback … they lacked a corkscrew.
US Military Vietnam Era Can Opener with Corkscrew