Yes it is but the major setback is transaction fees.
Bitcoin currently has a high value and the things people frequently shop individually from the supermarket is usually just a few $100 and it would seem uneconomical to send $100 with $2.6 for a normal fee that would be confirmed on time.
Plus even if you were to setup a lightning network only very few people know how to make use of it compared to people that could easily carry out a Blockchain transaction.
Using Bitcoin as payment option is gradually declining because it is now seen as a form of investment instead of P2P currency. It would only be economical to use Bitcoin in cases where the amount is huge.

Sure why not, but in the event of a banking failure your BTC is going to be just as worthless as dirt.
Unless the power company accepts BTC the servers will be off.
Unless their employees accept BTC there will be no staff.
Unless their suppliers accept BTC the shelves will be empty.

And so on.

You need the ecosystem 1st.

Same way you really can't bring gold & silver into the store to pay for things the way you used to. That ecosystem is gone.

-Dave

A supermarket chain has a central server to monitor loads of things such as stock levels, payments and customer traffic. If that server goes down, then it can cause problems for the supermarkets. My thought was that each supermarket could have ( may have) a local server to monitor the tills, cameras, stock levels and other stuff. Each of these servers could be used to facilitate payments and bypass the banking system. Bitcoin transaction fees could be a problem, hence the reference to lightning. Another option would be to use Bitcoin to fund an account or a gift card, and this could be used to make payments, although this may require connectiion to the main server. I'm really thinking of short term work arounds, rather than long term payment methods.

I think cash payments should always be available to everyone, even without internet connection.
In scenarios when internet is not working (especially in third world countries) the entire payment system could stop, so I think it would be good to have some paper bitcoin bills as a standard.
I remember one guy from Africa was very popular for developing bitcoin payments using dumb phones.

Sure it's possible but supermarket chains won't accept it unless it becomes very popular and people demand it, but I doubt that.
However, I am all for using off-chain offline payments with bitcoin.

Everyone knows that Bitcoin lacks on-chain capacity to cover the transaction volumes of even a small country. And Lightning doesn't have unlimited scaling either. And for people to start using Bitcoin in an emergence, they need to already own it, and how many people in the world are currently holding Bitcoin just in case banks fail? Probably almost zero.

As long as there is internet access then it would work. But you need to understand that a busy super market can’t accept Bitcoin because for 1 the fees at the moment might be high for the sender and the second reason is the confirmation times.

Even if the fees are low and network is not congested it might take over 30-60 minutes to get the confirmation. If they don’t wait for confirmation it would lead to double spends.

So I would say l2 solutions would be perfect for this. As they are cheaper and faster.

Usually in times of banking failure, the stores just inform the customers
right away that they would not be accepting any payment that involves the bank.
And if the customer does not have cash on him, that is his problem and not the
management.

I don’t see this happening unless the supermarket have an actual wallet that solely
Accepts bitcoin. Of course this is in context with a banking failure. Mass adaptation is a different story altogether.

It is technically feasible with lightning. However, that's under the assumption that you have a custodial mobile wallet with a few thousand sat in it. Non-custodially, this can't work practically. Nobody carries a lightning node in their phone, neither a mobile wallet connected to their lightning node running at home. And there is always the possibility that the payment will fail in the cash register.

On-chain is a no-go. You would pay a Big Mac for transaction fees alone. Also, customers can't be expected to wait 10 minutes (in the best case scenario!) for their order to finish. (The merchant can't accept 0-conf, because the client could just do RBF and double-spend it)

I read a bit about the news, and it seems that the most seriously affected thing was the online purchases and subsequent delivery orders. At least, Sainsbury's allegedly fixed the contactless payments pretty fast. With online orders, I think that even accepting payments straight onto a Bitcoin address would be fine. People can pay less than a dollar for a transaction, which isn't that much. But I suppose the legal implications of it in the UK (considering that cryptos are treated as assets, not currencies there) are just not worth it for the supermarket chains to try something like that.
I wonder why Tesco and Sainsbury's were both down at the same time. Does it mean that they use the same providers of some services, or was it a coordinated cyberattack?

Yes, for Bitcoin the price volatility would be a major brake for the company management to adopt it !

Maybe relaying on many crypto coins at once, so they can get a partnership with some exchanges to manage smoothly the thing! Especially that there is many blockchains now that are especially developed to handle big amount of transactions.

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But they need electricity etc. etc.

All what they can serve to in case of a very big solar storm is to transfer light beam though single segments to communicate by morse for example !