You CAN calculate a block and hash by hand.
So, you can spend your paper wallet on a paper block chain.

There are also several ways to wrap a coin, and then wrap a transaction, so that when you finally do get back to an internet, you can actually have the coins

But really, it all depends on how far society crumbles.
No electricity means no refrigerators, meaning many people are going to starve
Remember, food takes a year to grow

No fuel refining, no cars, no trucks, no deliveries.
Everything become VERY local.

So, cryptos are a good investment into a decentralized, technologically advanced society.

But, in all other scenarios, food and bullets are far better.

However, what i will tell you is that in the very near future we will have wireless internet everywhere as well as locally produced continuous green energy.

So, there may not be cars travelling everywhere, but we will still have communication that will not require any infrastructure.