At Busch, cash is still the backup plan. Enough is kept on hand in reserve that it can be distributed and used on short notice throughout the ballpark, but that's not a contingency that can be stress-tested very well.What is the contingency plan for any system outage? I have no clue how prevalent those are, but I could envision a 30 minute outage being a shitshow.
In-seat vendors and concession stands with traditional registers just pivot to cash for as long as they can. The real issue are the self-service kiosks that have popped up at 20% of our stands. Those are dead in the water if they can't run credit cards.
In the ticket office, we have a couple backup plans in place. A few boxes of pre-printed, $10 GA tickets that are designed to be torn on entry and even some of the old card imprinter devices we can get away with using in a real pinch. We shove all that in a drawer each season and hope it never sees the light of day. We keep about 50% as much as on hand as we used to for ticket sales, but we still have enough to cover an extended processor outage.