Which retail innovation was first widely implemented in US military exchanges during World War II, dramatically changing how soldiers shopped and influencing civilian retail after the war?

Military Post Exchanges (PX) and Base Exchanges have played a crucial role in military history, evolving from simple sutler wagons following troops to sophisticated retail operations. These military retail systems have pioneered innovations that later influenced civilian retail. Test your knowledge about a groundbreaking retail innovation that originated in military exchanges and changed how soldiers shopped during a critical period in military history.

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Self-service shopping (allowing customers to select their own merchandise without clerk assistance)
Catalog ordering system (precursor to modern e-commerce)
Point-based rationing system (early loyalty program)
Standardized global pricing (regardless of location costs)