Coconuts

Commodity money rides on communal agreement. Four castaways on a deserted island can form a commodity money system. Say the four castaways each claim a one quarter sector of the island for their own. One is a good gardener, one is a good fisherman, one is a good coconut picker, one is a good builder of thatch huts.

They need a commodity money so the fisherman doesn't have to carry his fish to the coconut picker when he wants coconuts. So instead, the fisherman carries a stick to see the coconut man. He takes four coconuts and the coconut man carves four notches in the stick. When the coconut man desires fish a month later, he carries his stick with the four notches back to the beach, hands it over, receives four fish in return.

Commodity money just has to be honest. The people on the island did not need to dig up gold to have a money system, just communal agreement. Fiat money fails not just because it is not directly convertible back into a real asset by the bank that issues it, but it also fails because its supply can be arbitrarily expanded outside the view of those using it for commerce, so the only people who can accurately fix its value are the counterfeiters of it.