I have managed in the UK to go around without Pounds. You can easily go around the UK with credit cards only. Even paying for a beer in the pub, a bus ticket, or a train ticket is just a question of using a credit card.
Last time I visited the US, I tried the same approach, but failed. Even toll booths were cash only. This was in Florida.
Soon I will be visiting San Francisco on a short trip and I don't want to be bothered having to look for an ATM or figure out how much money I should exchange.
So can I go around San Francisco without cash in my pocket and pay for everything with plastic?