Which innovative packaging feature was specifically added to American K-Ration boxes during WWII primarily for psychological rather than practical purposes?

During World War II, military packaging design was not just functional but psychological. Combat rations evolved dramatically from prior conflicts, with packaging innovations serving multiple purposes beyond merely containing food. These designs influenced military morale, logistics capabilities, and even post-war consumer packaging. This poll explores how military packaging psychology played a crucial role in supporting troops in the field during one of history's most significant conflicts.

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Camouflage patterns on the exterior to prevent enemy spotting
Printed games and entertainment on the inside of packaging to boost morale during downtime
Waterproof wax coating to protect contents in humid Pacific theater conditions
Perforated tear strips for quick opening during combat situations