Crypto currency is a extremely poor stand-in, since it is totally dependent on a mechanism for electronic exchange/transfer.
The obvious first casualty of any apocalyptic event would be electricity.
(EMP??).
Does anyone seriously believe the electrical grid would not be the first necessity to go. One need no further evidence that the Iraq War where they trashed access to power, water, etc.
How long would NYC, Washington, et al. survive before it would become a Mad Maxx Thunderdome. Laugh at the survivalists, but they can survive when the metro areas resort to even more Darwinian survival.
Essential material goods become the new "currency" via the original barter system.
Half the population would starve or dehydrate within about 30 days, from natural or man-made causes. Picture a WalMart doing pre-Xmas sales then multiply by a factor of 100,0000.
Remote/rural and self-reliant would be the only choice to survive.
Crypto - useless
Food supplies - limited to what you can carry and protect
Bartering - What do you have that is "valuable" to someone else.
Think Plymouth Rock in 1620-1621. Half died, but not from being killed by other Puritans
On a positive note, the surveillance state, corrupt parasitic government and evil banking systems would be obliterated. Marxist's will finally get what the wished for, but the "means of production" would be available to redistribute to the masses. Their plan presumes there is a "system" they can loot. In engineering terms, "a fatally flawed system" leading to chaos according to the effects of entropy.