Oh Wow, going on vacation. Hope you have a wonderful restful time!
When I take our furkids --three Yorkies and Boo the Boxer, I take everything they own -- they have more stuff than I do
Be sure to take enough water with you that they are used to drinking. Sometimes strange water can cause stomache upsets,
Wet wipes
A towel
Plastic bags for "accidents"
Paper towels
Spray air freshener
Treats
Harness and leash (I always keep harnesses on the kids when we are traveling)
Health Papers (be sure you know exactly where they are at all times--you can be required to show them)
Nutrical (you never know and it pays to be safe)
Something for fleas and mosquitoes
This is a "short list" just off the top of my head.