Which innovative retail practice was first widely implemented in military Post Exchanges (PX) during WWII before becoming standard in civilian retail?

Post Exchanges (PX) and their equivalents have been vital institutions in military life for generations. These unique retail environments have evolved from simple trading posts to comprehensive shopping centers serving military personnel and their families worldwide. This poll explores how military retail operations have shaped product design and customer loyalty in a specialized market with unique constraints and cultural significance. Test your knowledge about these distinctive retail operations that have supported troops from battlefield to base.

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Self-service shopping with shopping carts
Fixed pricing with displayed price tags (no haggling)
Inventory tracking with standardized SKU numbers
Customer loyalty cards with purchase points