[Supermancho]

There will always be a standard good for the basis of trade in proxy for government backed currency. The best choices will be durable (won't rot for a prolonged period of time), fungible (easy to convert back to digital cash), useful, and small to facilitate exchange at various magnitudes. Many choices will not fit cleanly and will all be less palatable. Notably, foreign physical currency, US stamps/bonds/checks, alcohol, or canned food would suffice. Ironically, a digital US currency should bolster alternative digital currencies.