Extra supplies of medication, medical records, a pet first-aid book and a first-aid kit. Ask your veterinarian for a mild tranquilizer to use in case of emergencies. (Rotate the medication regularly to keep the expiration date fresh.) Here's a basic list for your first-aid kit:
Comfortable bedding for the crate. A blanket can be used for the dual purpose of bedding and wrapping an injured animal in to prevent shock.
Cotton batting, gauze bandages and pads
First-aid cream - a triple-antibiotic
Food, can opener, water, bowls, litter pan and litter.
Medical records, pertinent information about your pet and phone number of your veterinarian. (Most kennels require proof of current rabies and distemper vaccinations before accepting a pet.)
Nail clippers, comb and/or brush.
Pet carrier or portable crate. (A collapsible metal show crate will accommodate more than one cat.)
Recent photos of your pet. Hopefully you won't need them, but if your pet is lost in the confusion, you'll want to place posters around the area without delay.