Which retail innovation was first widely implemented in military Post Exchanges (PX) during World War II before becoming standard in civilian stores?

The Post Exchange (PX) system has been a cornerstone of military retail for over a century, providing essential goods and services to service members worldwide. This unique retail ecosystem has pioneered innovations that later influenced civilian retail, while adapting to the specific needs of military personnel through wars and peacetime. Test your knowledge about this fascinating intersection of military history and retail innovation!

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Self-service checkout systems
Centralized inventory management using punch cards
Barcode scanning technology
Digital loyalty card programs