I know people out there who have invested a lot in gold under the belief that in the event of like complete societal collapse or hyperinflation, they could use it for purchasing.
I have the hunch it’s a scam, but I haven’t learned enough monetary theory, business, or economics to understand why.
And that would be doable, realistically. Though there’s a bit of plastic on the bottom that would be quite difficult to replicate.
The point is they’re only useful as a currency. And really only to a society that can’t really make much. If society advances again to the point where a used bottlecap can be replicated, other systems will already have been established to make it less attractive.