Just a disclaimer, I'm not actually on the Whedon Universe staff, just a volunteer, so I don't even know for certain that there will be a cash bar this year.
With that said, I personally don't drink, so I wasn't really paying attention to what they were checking for at the door. Plus I got into the ballroom early with the staff to help set up, so I didn't have to go through the door guards. But from what I remember, all they were checking for was badges. I think as long as you're not bringing something large like a six pack, you should be OK. Maybe somebody else has more information.
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