I always kept some cash on me just in case, but rarely needed it. I think most of the places were set up to take a room charge or credit card, some of the carts might only take cash though. I'd just keep like $20 or so in my wallet, that way I had it when it was needed.
I always though that too but I have read reports that even balloon vendors have portable swipe readers.
But OP you should still have some cash.
I think I carried the same 20 bucks around with me for the whole week. You don't need to carry much, but like others have said, it's nice to have a little cash just in case.
Actually, along these lines - Let's say I have my Disney Rewards card linked to my KTTW card. If I swipe the KTTW card in a place where there is a discount for using it, will I get that discount?