Hi! Unfortunately, I've had to use my first aid kit more than I would like...
I'm sure this is by no means a comprehensive list, but here's what I've used most often...
An extra leash/collar
A little first aid booklet
Flashlight
Gauze- non-stick squares and a roll
Wrap around self-sling bandage for holding gauze in place
Tape
Scissors
Antiseptic wipes
Betadine
Neosporin
Ice Pack
Most of our use has come from little boo-boos a such, so some gauze pads and wrap have been the go-to items we use...I keep one in the car and in the house.
Good luck!