What I keep on hand is very similar to LadyMom's supplies. In addition, I keep on hand:
NutriCal
Mineral Oil (for severe constipation)
Vaseline (for males stuck in the "out" position)
Canned/sliced white potatoes (for sick dogs)
Benefiber (dose is a pinch) (easier to keep on hand than canned pumpkin)
Topical Benadryl Stick
Probiotic (BeneBac is GREAT to have on hand, from Petsmart)
...I think that's it....