Keep I mind, the bigger tank you bring, the more water you'll need to lug around.
Melevesreef frag tanks typically hold about 10 gallons, and that's part of what makes them so appealing.
Anyhow, mike covered the basics pretty well. Make sure you price out your corals ahead of time, and if they're going to be hard to see them in the 20, then bring a laptop or ipad with pictures. You can even show off pics of the colonies.
Cut the frags now, so they have time to heal.
Transport of the corals is a biggie. The less they get banged around on the way to the show, the better. Especially zoas.
Create a rack of egg crate that not only fits your tank, but fits a piece if Tupperware properly. That way, you can lay out the frags the night before, price them, and then just pick up the tray and move it in the Tupperware and then into the tank.
Hope this helps