Which retail innovation was developed during WWII that revolutionized how products were delivered to frontline troops and later influenced civilian retail operations?

Military Post Exchanges (PX) and Base Exchanges (BX) have a fascinating history of retail innovation. These military department stores have evolved from simple sutler wagons following troops to sophisticated retail operations serving military communities worldwide. This poll tests your knowledge about a pivotal retail innovation that transformed how military personnel accessed goods during wartime.

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The K-Ration System - pre-packaged meal kits with standardized pricing regardless of location
The Mobile PX - truck-based retail stores that brought products directly to forward operating areas
The Scrip Currency Program - a cashless payment system using military scrip instead of local currency
The V-Mail Catalog - allowing troops to order products via standardized letters for delivery to the front