Maybe instead of using terms like “currency” or “money”, its better to think in terms like “a medium of exchange” because the circumstances will determine what is of value to whoever you wish to conduct business with. A hungry person likely will not be interested in a Gold Eagle if they know they can’t readily exchange it for food. But a couple tins of canned beef might work.
The FRN will still be valuable, at least initially, even though its fiat and has no real backing. We should think in layers – cash (until it no longer has value and people refuse it), tangible trading goods (when those type items have value because they meet immediate needs), and PMs (for when some system is organized and back in play).
As for where to store any of it, thats up to the individual. Sharing ideas in that regard could come back to haunt those making the suggestions.