Turns out things get wet really easy in the jungle. They learned this in the Vietnam and so bright spark came up with these plastic bags for your M16 magazines.
The bags could be reused and had an emergency break away on one end. The other end has a sort of bread tie made into it. You insert the mag, roll down the end and use the bread tie like wire to fold it over to make it water resistant.
Some even brighter spark decided to print a propaganda message on the bag, Knowing troops would discard the bags and leave them laying in the jungle, it was possible a defector might pick it up and decide to defect.
The message is in Vietnamese and basically says surrender to the troops of RVN and use the bag to get safe passage.