Two comments.
First, any table coverings should meet fire codes. Weed block does not; I would test a black plastic tablecloth before using it.
Second, Paul's and Andy's lists include way more tools than I bring for a show. Different people want to do different things at shows. I want to run trains. If an engine has an issue, my preference is to fix it at home and run a different engine at the show. If a module doesn't work, spend a few minutes to try to fix it, but swap it out if it's holding things up. Show time is precious - I don't want to spend it troubleshooting!
I agree that a first aid kit is a good idea. A stash of Band-Aids keeps blood off the modules, especially on an N-Trak layout where rail joiners sometimes penetrate skin.
My two cents, for what it's worth.
Geoff