In times of real crisis, only hard assets like gold and wanted assets like cigarettes and toilet paper. Hard currencies like the US Dollat may be desirred as well in case the crisis is local. What I see as a plus of cryptocurrencies is the flexibility in securing and shielding off your stash and taking it over the borders.

But in a real Mad Max scenario (worldwide total societal collapse), cryptos will be useless. With no meaningful social cohesion left, one is more concerned with not dying.