In the South Pacific, there were "rai stones". I read (but now cannot verify) that many of those stones were very large, and a tribesman "owned" one. He knew which one, and it signified his wealth. Then the Americans came during the War, and cleared them for an airstrip. Totally messed up their economy because now they didn't know which stones were which. Or so I read a few decades ago.

Though the wiki says that when the Japanese first occupied the island, they did a lot of damage by using their stones as building materials.

They aren't used any longer, of course. But it does show that people can agree on anything as a mode of trade. The most common one today is gold, even if most currencies are only partially backed by gold. Should the excrement hit the fan, civilization crashes, cash and/or gold will be useless. It will be barter for some time before people start minting currency acceptable to the masses (what's left of them). During such an upheaval, I wouldn't be likely to survive anyway. 1poorlady also. We're getting old, have meds we need, etc. So it's not an issue for me. Despite what William Devane says, buying gold won't help me at all.