I think you're referring to C-Rations. They had the P38 and small quantity cheap toilet paper. The sundry packs were large boxes of stuff as I mentioned above. That's where I remember finding those plastic razors. The C-Rations had food, a chocolate disk, mini pack of cigarettes (4), P38 and toilet paper.I did two tours in RVN, as a grunt. Plastic razors(I think they were black) were in the sundry packs. Most of the guys in my outfit had DEs but left them in base camp.
Shaving wasn't done much in the field.
Funny thing about those sundry packs, you'd get a new P38 can opener in each one, but only a few sheets of toilet paper. P38 could be used many times until you lost it. TP could only be used one.