Players can convert each Pre-War money into Cloth, a useful and hard-to-acquire crafting component. We say almost worthless, because there actually is a reason to collect Pre-war money in Fallout 76, and it's not just about hoarding useless cash. Normally represented as thick wads of bills, the money that would once have been vital is almost worthless after the nuclear war. However, although Bottlecaps are the new currency, players can still find Pre-War money in Fallout 76. They were adopted because of their relative scarcity, and because they were hard to counterfeit with the Nuka factories having been destroyed in the war.
Following the nuclear holocaust, the caps 0f Nuka Cola bottles became a de-facto currency among the survivors. Bottlecaps have replaced dollars in Fallout 76, as well as in the rest of the Fallout series.