I am not disagreeing that cash will be used less, I am disagreeing that we can move to a cashless society.
I'll buy you a meal, for cash, if I can't go for a month without using cash. I already go for several weeks without using cash, but am stopped by some of the small traders at the farmer's market. But more and more of them are taking cards, and I'm getting close to the point where I simply won't bother going to the stalls who make it difficult for me to pay them, and if there were a meal at stake, I'd just buy different meat.
Going further, I believe I would probably be able to leave the house carrying only my phone, today, and, aside from the issue of keeping it charged, function for a month without any other form of payment or ID apart from my work pass. I'd need a driving licence in order to fly internally or drive, a passport to fly internationally, and I'd want to check my offer of a meal if I needed to go abroad and couldn't choose where I went (Apple Pay works fine in many places, but isn't anything like universal).
Outside payment, I'd need my driver's license or passport to fly, and it would be wise to have it when driving, and I'd need a debit card if I wanted to collect advance purchase train tickets (although increasingly I can buy them straight to my phone, so I'd be able to make most journeys, albeit perhaps with slightly more restrictive tickets, using just the phone). Otherwise, I think can do everything with the contactless cards loaded on to my phone.
I'd certainly be willing to live for a month using only a phone, my passport and one debit card now if someone would . I can't think of anything I do which would be more than a