Which packaging innovation was introduced in the K-Ration during WWII that revolutionized food preservation for combat conditions?

During World War II, packaging design became critical for military operations. The development of combat rations represented one of the most significant packaging innovations of the era, changing how armies were supplied in the field. These innovations not only addressed immediate wartime needs but also revolutionized civilian packaging technology in the post-war period. Test your knowledge about one of the most famous military packaging innovations that changed battlefield logistics forever.

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Waxed paperboard boxes that could be burned as fuel after use
Laminated cellophane wrappers that maintained freshness in extreme conditions
Self-heating metal containers activated by salt water
Color-coded tins that indicated caloric content for different activity levels