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

Military Post Exchanges (PX) and Base Exchanges have been vital retail operations supporting armed forces for centuries. These military retail networks evolved from simple sutler wagons following troops to sophisticated global retail chains. This poll tests your knowledge about how military retail operations revolutionized civilian retail practices with innovations that later became industry standards. How much do you know about the crossover between military retail innovations and today's commercial retail landscape?

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Self-service shopping (customers selecting their own merchandise without clerk assistance)
Barcode scanners for rapid inventory management
Loyalty card programs for repeat customer rewards
Standardized pricing across all store locations