Just a word of warning. I always carry a back up. I have been to the festival more than once when the tragic band system went down. While it was very nice for those of us with Other payment methods as they were no lines, there were a lot of rather upset people who could not buy food because the system would not work.
Just last month I was at the Les Halles in France. And they had stationed a woman at the entrance to explain that you had to pay cash or use a credit card. Several people in front of me the stormed off angrily because They couldn’t use their magic bands