Given the number of tanks you have reserved a the show, and the size of those tanks (6',7', 8') plan in advance which fish to take. As the show draws near, set up your QT (if it is not already running). I have our QT filter sitting on the edge of the main pond getting primed right now for a show in mid Sept. I will setup up our 8' show tank a couple days before the show. The I take my time and move those fish from the pond to the show tank. This is when I refine the preliminary list into the final candidates.
It is SSSSOOO very much easier to bag and box early the next morning from the QT than trying to track everyone down in the big pond. Naturally we are not feeding for at least one week before the show. I also put a pinch (like a kitchen match head amount) of Elbagin in the bags. Just enough so the water looks like Mountain Dew.

A little dab will do ya.
Also I use tie wraps (plastic cable ties) to seal the bags. No breaking rubber bands, no tired hands. Get the BIG ones (18") so you can really tighten them well. I use those on inner and outter bags. I do NOT trim the ends of the tie wraps. Those sharp ends could pierce a bag.