How could we have offline transactions?

When comparing cash to crpyto and specifically ethereum, I notice that there still a big portion of classic fiat that is left out in our usual discussions and development.

Namely, offline transactions.

When comparing digital fiat banking to crypto, crypto is similar enough. Often, all you need is just a internet connection to send and receive crypto and make txs.

However, we haven't covered most of the txs possible with cash in crypto. One of the main things is the simplicity and ease of cash. Are you hiking with a group and you want to give them 5$ for the shared food? Just give them 5$! No need for an inet connection in the forests there. Or are you in a developing country where internet access is sometimes bad or non-existent? No worries. Just use cash and make transactions without any complex technology.

I think these use cases of offline transactions are largely untapped in Crypto (as far as I can tell).

My question is: What can we do to make this happen? Or how much demand would there be for such a thing?

Of course most people in comfy chairs in a developed country won't really need it. But even then, often cash is quite simple and easy - and so should also crypto enable offline transactions.

I haven't thought too much about how to implement this in ethereum. I don't know, whether this can be an entire wallet software only thing, or whether this needs a protocol change.

Looking at the gist, it should be possible, right? You could have two wallets on the two smartphones which can connect to each other. The sender A can sign a transaction saying that A sent x ETH to B and the signed tx would then stay unconfirmed in both the smartphone. The balances in both smartphones update and both can make more subsequent offline transactions. As soon as one of these smartphones connects to the internet (after the hike), the signed txs are submitted and the local unconfirmed txs are confirmed on chain. This would be a general first approach.

Obviously, there are still many open questions. E.g. how to create the tx not knowing the gas prices? How deal with a tx rejection, if the sender balances turned out to be insufficient when connecting back to the real Blockchains as concurrent txs were done? And how can we make certain txs possible (p2p send ether), but not others (uniswap swapping tokens, which needs current rates).

What do you think about this? I would be interested in being able to use such a thing - and with growing adoption, this becomes more relevant as I can tell.