At our pre-comic con prep party, someone showed up and showed off his new shopping wagon. It's 3 feet long and 2 feet wide. He told me that he was going to use this cart at the comic con "so I can carry all of my purchases at the same time."
He reappeared last weekend at our local gaming convention. To be fair, his cart was half full with about 8-10 board games. However, he parked the cart directly in front of a flea market table and left it there blocking access for 30 minutes. I would have said something but I was working elsewhere in the room.
What can I say to the convention operators before this becomes as common as the carts and bags at GenCon? By the way, at this gaming convention, your car is always less that 200 feet away from the vendors' hall.
(We also had a few giant backpacks, but they are few and our hallways are wide.)