In a temporary crisis, cash on hand has real value. But ...
Most of the concern is about a SHTF or TEOTWAWKI scenario — longer lasting.
What this implies is that CASH, coinage, precious metals has/have a limited shelf-life. Traditional currency will quickly lose value when needed items are disparately scarce — meaning barter takes over, I trade what I have (that you need) and I get what I really need and you can spare.
Cash on hand allows you to bug out or stock up in the first 36 hours. in the first day, travel will be OK. In the second day, travel will be difficult and risky. On the third day, travel will be treacherous and deadly. ... and traditional commerce will be gone for a LOOOONG time. No need for cash after four days.
SO ... cash is arguably valuable only for the period when banks fail/shutdown (for whatever reason, including grid-down) UNTIL “realization” sets in and rational, civil commerce ceases. After that cash and metals will not, in my opinion, be valued for trade.
As many folks here have suggested, security (arms, structures and tactics) food, clothing, water, shelter, health/hygiene items, work/labor skills and sex will be the currencies. Cash will only be good until people REALIZE the SHHTF. Once ‘they’ get past their normalcy bias and see the realiy ahead of them, the real currencies will immediately emerge.
IMHO.