Bring a notepad and a pen and have people sign in.
Last year, we arrived at 7:00pm the night before, and there were about 15 people in line in front of us. We started talking about the riot that usually happens the closer it gets to opening. I am from ND, and it is usually 10-25F, so there are people in tents and whatnot, so it is hard to keep track.
We numbered a paper from 1-100 and put our names down. As new people came, we flagged them down and had them sign up. Of course, once there are a lot of people there, it becomes pointless. Anyway, when it came time to hand out the ticketed items, there were a lot of people making sure people in front of them were on the list, and we used it to keep the "cutters" out.
