Here are some good things to have in a show kit:
Paper towels (for cleaning up small dirty spots--just dampen them with water. Also helpful for wiping off your hands when applying oil, etc)
Baby wipes (the same use as paper towels--great for wiping off feet)
Some sort of oil (for making combs shiny)
Antibiotic ointment (I've found that this moisterizes combs well, and it can be used in case your birds get into a fight)
Poultry Protector (I use this to spray down the cages that my birds are in, to help reduce the possiblity of them getting mites. You could also use vinegar.)
A cup (you can use this if you have to carry water to your birds, or to hold water when dampening a paper towel, or to hold cotton swabs for applying oil. A cup has many uses.)
Cat nail clippers (you should have all of your birds nails trimmed by the time you go to a show, but if you miss some, you'll need nail clippers)
Human nail trimmer (this is for last-minute trimming of beaks, etc)
Silk cloth (This can be used to shine up your birds. Run it over the feathers, and it will make them shinier. Especially good for black birds or parti-colored birds)
Hope this helps! And, good luck with your show!