You are being flippant. What if for example a massive cyber attack took the whole electronic payments system for days? The economy would grind to a halt. People wouldn't be able to buy food. There may well be looting.
Like most people I usually pay electronically but I would like to retain the option of paying in cash if I want to. What's wrong with that?
This was a Sainsbury problem, not a problem with the whole EPS system. A case of human error, not a systemic EPS problem. Someone in Sainsbury made a bad decision and I'm sure lessons will be learned so that a repeat will be even less likely.
There were plenty of other supermarkets nearby so I went to another and bought some groceries with a wave of my phone.
The possibility of cyber attack on the EPS is so much talked about that so many precautions are being taken against it that something else would probably be a greater threat.
It would be very hard to take down the entire electronic payments system. It is run on IBM mainframes each with 40 terabytes of RAM with many layers of resilience including geoplexing - ie multiple copies of the system at different secure locations. Those mainframes are even immune to interference from cosmic rays.
In the case of Sainsbury I read in the press of disruption and wanted to check it out for myself. At my local susperstore there was printed signage and a group of staff ready to help at the entrance - noone was speaking to them because I guess noone was having problems - the place was otherwise as normal with the aisles thronged with shoppers.
I never go out without a tiny flat wallet as a backup, even though I pay for everything with a wave of my phone. Yesterday I checked the wallet - couldn't remember if there was any cash in there as it's so long since I looked - but there was indeed a wad of tens and twenties.
Couldn't be bothered with cash and Sainsbury's Nectar prices were also down, so I went elsewhere. Plenty of other supermarkets all working as usual.