And yes, in a zombie apocalypse (assuming internet and electricity) cryptocurrencies have an advantage over gold, because it's easier to carry, to transmit and to keep.
I would say there is even space in post-electrical (once the centralised power switch is pulled off) world for crypto-currencies.
If there are groups of people hoarding electronic equipment and amateur radio stations plus modems, they will be able to operate Bitcoin or rather a POS cryptocurrency long after the switch is off.
They will have small local generators and connect to each other over radio.
In their communities, they will issue notes backed by Crypto.
Perhaps, they will be called "priests of Bitcoin".
If that were to be true, we'd be looking at a world, in which crypto is more valuable than the energy necessary to keep the network running. But, if the power plug is off, wouldn't the energy source itself be more convenient as a mean of exchange? You can't run engines on crypto. You can run crypto generator on aforementioned engines.