Sad that you insist on paying a 3% tithe to the payment processor companies instead of bothering to carry a few pieces of paper around. This hurts your local, small businesses.
I have to know beforehand how much I'll need, and keep that separate from the rest of my funds. This means that I can't use it for anything that would normally come directly out of my account, and can only be used for in-person transactions.
You are over-simplifying the entire process.