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

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. These military department stores have evolved dramatically through wartime and peace, introducing numerous retail innovations that later influenced civilian commerce. Test your knowledge about this unique retail operation that has supported troops from World War I to modern conflicts.

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Self-service shopping format
Barcode scanning technology
Loyalty card programs
Point-of-sale computerized registers