Which packaging innovation was first widely implemented in the US Army's K-Rations during WWII that revolutionized field feeding and later influenced civilian food packaging?

World War II saw remarkable innovations in military packaging design that influenced consumer goods for decades afterward. The K-Ration was a groundbreaking development in compact, lightweight combat feeding that had to balance nutritional needs, preservation requirements, and battlefield practicality. This poll explores the packaging innovation that made K-Rations particularly revolutionary for their time and changed how soldiers received sustenance during combat operations.

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Waterproof waxed cardboard boxes that could float in water and withstand extreme temperatures
Aluminum cans with pull-tab opening mechanisms that required no tools
Glass vacuum-sealed containers with rubber gaskets for extended preservation
Self-heating containers using chemical reactions activated by water