Which retail innovation was first widely implemented in military Post Exchanges (PX) before becoming standard in civilian retail during the post-WWII era?

Military exchanges (PX/BX stores) have been crucial to troop morale and welfare for over a century. These retail operations have evolved from simple sutler wagons following armies to sophisticated global retail networks supporting military communities worldwide. Test your knowledge about how military retail operations have shaped both military life and civilian retail practices throughout history.

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Self-service shopping model
Barcode scanning technology
Credit card payment systems
Computerized inventory management