The marines on Guadalcanal became quite skilled in counterfeiting red “meatball” Japanese flags which they traded to sailors unloading supplies on the beach for candy bars and other products.
It happened in Viet Nam too. There was a Special Forces camp we occasionally resupplied. We’d trade “necessities” like women’s stockings and underwear for “genuine” VC flags and sandals. These we’d trade to the navy for real ice cream, real milk and other goodies. Our navy had great rations.
I heard a story about Walt Disney, a WWI ambulance driver.
He'd collect German helmets, and shoot them, the bullet holes "adding value" and cachet to his souvenirs over his competitors'.