I think this whole thing of feeling secure because I gave gold to replace the paper dollar is kind of spooky and unreliable. In other words, hopeless.
And how do you dare reveal to the butcher, the baker, or the candlestick maker that you have a supply?
The problem, under the Mad Max scenario, won't be using it.
It will be keeping it.
You start you premise with - the dollar is worthless. So in that case, what can you do with dollars beside use them as toilet paper ? At least gold will retain its value. Worse case scenario, you sell a gold coin for paypal credits. Then go down to the local grocer and slide your paypal debit card for payment. My guess is we will have a gold or silver backed online service. How about paygold or paysilver ? Eventually you will be able to buy groceries with silver eagles. Otherwise known as, real money.
Your question implies a collapse of government currency. In such an apocalyptic case (which will not happen), you arrange for the gold to be held as collateral in a credit account with whomever. Exchanges would spring up in no time, probably organized by banking institutions. Local scrip would replace the dollar for small purchases, as it did during the Great Depression, only now based on gold held in trust by third parties rather than on full faith and credit of the goobermint.
There is an extra premium but there is also greater flexibility.
Also look at silver, especially junk silver. A mercury dime is worth about $3 in meltdown value of the metal at silver $40 an oz, a silver quarter (pre 1964) is worth about $7. That is maybe worth a loaf of bread or a gallon of gas or a bottle of aspirin.
Even pure copper coins are heating up- copper is $4 a pound but who gets to buy and hold industrial copper and who wants to try to trade in big bars of metal? Coins are $1- $2, have the chance to become the poor man's silver (as silver is the poor man's gold)
Our society is used to seeing gold silver and copper (esp coinage) as money and as having value.
“How do I buy groceries or puchase gasoline, etc. with my gold coins?”
Answer: You wouldn’t use gold for such small transactions. Rather you would use silver coins (nickles, dimes, quarters, half-dollars and dollars).