I'm always tweaking my dog's kit, too, so I know how you feel. KenK is right that many supplies you probably already carry on your person will work when administered to your dog.

Our mutt, who is only 10 lbs.,travels with us alot, so he rides in a Sherpa pet carrier. His kit resides in a very small bag that attaches to the handles of the Sherpa bag and so far contains:
-Tiny tube of Superglue (for closing cracks and splits in the dog's paw pads)
-Small mouth syringe (for giving him meds) and his meds
-Tweezers
-Conforming gauze
-Dog booties
-A quart-sized Aloksak with 3 days worth of food (this can be stretched out for longer, too)
-Leash with waste bag/dispenser attached
-Harness
-Set of plastic fold-up dog bowls
-Hamster water bottle (for giving him water while he's still in the bag)
When adventuring I can easily detach his kit and throw in my pack, as it takes up very little room.

I've got small scissors on my Leatherman to clip his fur if necessary (and which have worked really well on him in the past), and any indigestion or painkiller meds he may need reside in my FAK. Just make sure you read up on what quantities are safe to use on your dog.

You may want to talk to your vet about animal first aid classes. He or she may be able to point you in the right direction, or be willing to host some for clients themselves.