Personally I wouldn't buy one at the expo (sorry to be a downer). They are extremely stressed and either shoved into a cage with a bunch of others where they could transmit diseases back and forth, or they are in deli cups, which is just horrible for them. I've been to several shows over the years, and nothing has ever made me change my stance on this.
If you do decide to do it, and you have to spend the night somewhere, bring a shoebox with a fake branch and a small towel to place on the bottom of it. Place your new friend in there and bring them into your hotel room. Put it on the desk, or by the TV and put something on top where air holes aren't blocked but it's heavy enough to keep your new little one from escaping.
For the car ride home have a fabric laundry pop-up hamper with a fake vine zip tied in it for the ride, and a towel at the bottom. My guess is you will be far enough away that the ride would be a couple of hours if you think you might have to spend the night. Shorter rides the chameleon could stay in the shoe box.
