The lockers at my local swimming pool only take pound coins, so I always keep one separate, and don't spend it on anything else.
I do find it off putting and bordering on the offensive to hear someone who prefers cash described as a "cash zealot", and equally it is derogatory to refer to someone who prefers to use cards as an "anti cash zealot".
People prefer different payment methods for a whole host of different reasons, and I think everyone should have the choice about which payment method to use.
I don't like a business dictating to me what method of payment I should use.
Cash is very useful if you are going to the pub and don't want to drink more than a certain amount. If you know that a pint costs £4 and you want to drink no more than three pints, you can take £12 in cash and no cards or phone, and then it is impossible to have more than three pints.
I was in a coffee shop in Birmingham a few weeks ago and when I offered cash they said it was card only. But I noticed that they had a tip jar on the counter which contained, er, ..cash. So you can accept cash for tips, but not for people who want to pay for a coffee. I find that hypocritical, and needless to say I didn't give them a cash.
Of course one factor in the decline of cash usage is the closure of many bank branches, with their associated cashpoint machines.
When I moved here nearly four years ago, there were two banks, plus a supermarket and a petrol station with a free cashpoint machine. When the first bank closed, they said you could use the cashpoint at the bank on the opposite side of the street or the one in the supermarket. When the second bank closed, they said you could use the one in the supermarket or petrol station. Then the supermarket closed, and the only one we have left is in the petrol station.
I think cash usage will decline, but I don't think it will ever die out completely. We have seen instances of banking apps and Wifi going down, rendering card payment machines inoperable