Which retail innovation, initially developed for military purposes during WWII, fundamentally changed consumer psychology by introducing the concept of 'self-service' shopping that became standard practice in post-war retail?

Throughout history, military needs have driven retail innovations that later transformed civilian markets. From preservation techniques to supply chain management, warfare's demands created lasting impacts on how products are designed, marketed, and sold. This poll explores how a specific wartime retail innovation changed consumer psychology and shopping patterns for decades after the conflict ended.

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Supermarkets with shopping carts (allowing customers to select their own goods rather than requesting items from clerks)
Mail-order catalogs (enabling remote purchasing of standardized military surplus)
Installment payment plans (helping families afford expensive goods during wartime rationing)
Product packaging with nutrition facts (developed to ensure proper caloric intake for troops)