Which retail packaging innovation was specifically developed during WWII to better supply combat troops and later revolutionized civilian retail?

Military exchanges (PX/BX) have a fascinating retail history dating back to the early 1800s. These specialized retail operations have evolved dramatically over time, from basic sutlers' wagons following troops to today's modern department stores serving military communities worldwide. This poll tests your knowledge about a significant retail innovation that changed how military personnel shopped during wartime.

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K-ration boxes with integrated moisture-proof packaging
CARE packages with compartmentalized product sections
Aerosol spray cans for insecticide and food products
Vacuum-sealed tins with pull-tab openings