here's what you do at sdcc. don't bring your credit card and stuff $7000 in your wallet. then you're set
Nice to see the lime green be represented again at SD this year! Gargamess was that exact same color last year !
It varies from booth to booth but cash works best all around. If I recall the ATM at the convention center doesn't have terribly unreasonable service fees but there is ALWAYS a massive line for it (ditto on the Starbucks) and konks out from time to time. Save some time and find an ATM near your hotel before you get to the convention center. That blue Smogun is super tempting...
You definitely should not count on being about to use credit cards. Having a wad of cash on hand is the best strategy.