I would advise bringing cash just in case. You will definitely need it for parking ($3), and some vendors offer better prices if you pay with cash. There is an ATM right inside the gates, though!
Parking is $3 cash. Cards are accepted at most vendors there's an atm inside the front gate.
You can buy tickets with a credit card and most (maybe all) vendors take credit cards. There is an ATM machine just inside the front gates just in case you decide you NEED a $300 sword and they only take cash.
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