Alot of people in this thread really haven't looked into world history. One of the most repeated cases throughout history, is that whenever a society completely collapses, fiat currency issued by whatever authority, eventually becomes worthless. On a base level, things crucial to survival are essential, guns/ammo, other weapons, food, shelter, etc. Bartering for goods/services is the norm until a new authority is established. It goes like this every single time without fail. Reichsmarks during WW2, where they were more valuable for kindling than currency. The Dinar during the Bosnian war in the 90s, where the entire area was essentially barricaded, money was worthless, and the locals were left to fend for themselves in a war torn Mad Max type hellscape, and any number of African civilization collapses. Of special note are the
Hungarian million billion bank note, and the One Hundred Trillian dollar Zimbabwe note as extreme examples of hyperinflation when an authority collapses.
Precious metals and gems are unique in that they always tend to hold some sort of value, even if it's for future use. That's consistent throughout recorded history, while obsolete currency usually only holds value for it's historical significance. Even then, common coins were often melted down because the precious metals used were seen as more valuable than the coins that were minted from them.