Alcohol, peroxide, betadine scrub solution, tramadol, vet wrap lots of vet wrap!, splints precut to length of each dog legs to support a broken bone, blood stop (for horses powder) white adhesive sport wrap, big gauze pads. GasX, Digel anti-acid, Anti diarrhea, benydril liquid.
And IMHO the most important is a 'muzzle' for 'each' dog on board that fits properly on each dog.
When they get hurt badly they are not the same warm fuzzy pup you used to know. And you need to get in there and apply first aid asap and the muzzle will allow you to do that.
My first aid kit is far more in-depth then what I listed but then again I feel you can't have too many first aid items in case of an emergency.:C