Which retail payment innovation was first widely adopted by US military exchanges (PX/BX stores) in the 1970s, nearly a decade before becoming common in civilian retail?

Military exchanges (PX/BX stores) have been a crucial part of military life for generations, providing troops with tax-free goods and a taste of home while deployed. These retail innovations have evolved from simple commissaries to sophisticated shopping centers that generate billions in revenue annually. This poll explores an interesting fact about how these military retail systems helped pioneer a payment innovation that later became widespread in civilian retail.

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Credit card acceptance
Electronic barcode scanning
Debit card point-of-sale systems
Self-checkout kiosks