Last year I used my CC and even a Disney gift card at some snack carts. There might be some carts that don't take cards, but I am not sure since the ones I went to always took cards.
There were quite a few times that I went to snack carts in the evening and the system was down for some reason, and they couldn't take cards of any kind. The first night it happened I didn't have any cash on me. The next night the same thing happened and the system was down, but this time I remembered to get some cash to bring into the parks just in case.