Which retail innovation was first widely implemented in military exchanges before becoming standard in civilian retail?

Throughout military history, post exchanges (PX) and similar military retail operations have played a crucial role in troop morale and military effectiveness. These unique retail environments have evolved dramatically over the centuries, from simple sutlers following armies to today's modern military department stores. This poll explores how retail innovation has shaped military operations and influenced civilian retail practices.

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Self-checkout kiosks
Universal product codes (barcodes)
Fixed pricing (no haggling/bargaining)
Loyalty reward programs