I know this is a hot button topic, but here goes.
I was always in the "of course you should have cash when you're on vacation" camp and, well, I still think you need some but not nearly as much as I used to. As of last month, everything in London is tap to pay. Yes, everything. I'm a serial candle lighter in cathedrals and always made sure I had coins and bills; not necessary, there's a tap to pay terminal right there. Even the buskers in Trafalgar and in Bath had small terminals set up so you don't need to throw money into their guitar case.
The only exception I saw was a restaurant in Chinatown that had a sign on the door that said CASH ONLY. Boy did that catch a lot of people by surprise, skidding to a halt before entering.
So cash if you wish, I still will, but it's so not necessary. Another change brought to you by Covid.