If you don't think bartering doesn't work, I have a shiny diamond ring for you, if you're willing to change your mind.
(more seriously: I think people are going for a substantial reduction in practical feasibility more than anything. The inefficiency of barter is unlikely to affect that.)
Given the fanaticism of the gun debate, if laws don’t prohibit the medium of exchange, you can bet that anything from scrap copper plumbing and wire, to lumber, to livestock would be accepted in some circles, in order to breathe life into a market with enough demand.