Which retail innovation was first widely implemented in military exchanges (PX/BX) during World War II that revolutionized the supply chain for troops?

Military exchanges (PX/BX) have been a crucial part of military life for centuries, providing essential supplies and a taste of home for service members worldwide. These unique retail operations have evolved significantly from their origins as sutler wagons following armies in the field to modern, sophisticated retail chains. This trivia question explores how military retail operations adapted during a pivotal moment in history, balancing logistics challenges with troop morale.

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Self-service shopping (allowing troops to select their own merchandise rather than requesting items from clerks)
Catalog ordering system with delivery to field positions
Integrated credit card payment systems for military personnel
Computerized inventory management using early IBM punch card systems