Which historical military retail innovation was first introduced during World War II and revolutionized how troops accessed products in remote combat zones?

The Post Exchange (PX) system has been a crucial part of military life for generations, providing essential goods and services to service members around the world. This unique retail ecosystem has evolved from simple sutler wagons following troops in the 19th century to modern, sophisticated retail operations. Test your knowledge about this distinctive aspect of military retail history that has supported troop morale and readiness for over a century.

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Mobile PX trucks (nicknamed 'rolling stores')
Aerial delivery catalogs (allowing products to be parachuted to forward bases)
Battlefield subscription boxes (monthly essentials automatically shipped)
Token-based exchange system (replacing cash transactions in combat zones)