Which innovative retail strategy was first widely implemented during World War II to boost troop morale by providing familiar American products to soldiers overseas?

Throughout military history, the Post Exchange (PX) system has been a crucial element of soldier morale and military logistics. These retail operations have evolved from simple sutlers' wagons following armies in the field to sophisticated global retail networks serving military communities worldwide. This trivia question explores a significant innovation in military retail history that changed how products were delivered to troops in combat zones.

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The PX (Post Exchange) ship-to-shore delivery system
The Army Exchange Service's 'Follow the Troops' mobile retail units
The K-ration retail supplement program
The Army & Air Force Exchange Service's (AAFES) 'Warfighter First' initiative with standardized pricing