Which retail innovation was first widely implemented in US military PX stores during WWII that revolutionized military retail and later influenced civilian retail?

Throughout military history, supply chains and retail operations have been crucial to battlefield success. The modern military Post Exchange (PX) system revolutionized how armies supply their forces and maintain morale through retail innovation. This poll tests your knowledge about how retail strategy evolved to support military operations and how brand storytelling within military retail has shaped military culture and effectiveness.

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Self-service shopping (allowing soldiers to select their own merchandise rather than requesting it from clerks behind counters)
Military-exclusive branded products (specialized versions of civilian goods with military branding)
Fixed pricing system (eliminating haggling which was common in many overseas markets)
Catalog ordering system (allowing soldiers to order items not stocked at their local PX)