I've always assumed you'd melt the gold down and create coins or other tradable sub-amounts of the gold that you could exchange for goods and services. If people are still peopling, they'll still want a currency to transact with; if the dollar has failed then gold has a historical precedent that would probably make it easier to convince people to trade with you using it as a medium of exchange. It always seems like it's more suited to be an emergency measure than a plan A to me.