Jewelry isn’t the best exchangeable commodity because the value of the items is too subjective. Gold and silver (or even copper/bronze) coins (or privately-struck metal rounds) fit the bill because they are a standard size, weight and metal content and both the buyer and seller can easily understand what they are getting.
I can see private mints issuing bars and medallions doing a roaring trade if a serious transition towards ‘all-digital’ money is made...
Well they guy who made Silver Liberty coins got arrested. Seems the FedGov wanted no part of someone making "Barter Coins"