I was a boy scout so I follow the "be prepared" motto.
For those with cats who for whatever reason can't get there cat to a vet in an emergency (be it money, location or timing, which means everyone) here's a few items you should ALWAYS have ready in the house for use in case of an emergency. This especially applies to those who pick up a cat/kitten on the street:
1: Amoxicillian. A few pills will do it, just one or two even. It's a safe antibiotic for a cat, and most human strength pills are strong enough that one pill can be ground down and used for 20 or 30 doses. Infections pop up suddenly and can do permanent damage, especially to the eyes.
2: Some form of pain killer (barbiturate or opiate). Hopefully your cat will never need it but you never know. Inject in the rear leg upper muscle or use a feeding syringe if possible.
3: Cat carrier. A cheap plastic one is good enough. Good for locking kitty up in medical emergencies, or emergency moves. Don't use the cardboard carrier if the cat's more than half grown, they can tear their way out in seconds!
4: Collar and leash. Unusual for a cat, but if you have to catch an "escapee" or move kitty, a safe way to keep him from making a break for it!
5: Pepto bismol. Used in TINY amounts is helpful for stomach problems. A few drops only.
6: Athlete's foot cream. Same stuff that's in ringworm treatment.
7: Mother's Milk Replacer: We like to keep the second stage formula around. It's great for cats who are off their feed.
Anyone can think of other useful stuff, let us know. Like children, cats seem to specialize at getting sick at 1AM in the morning, usually a saturday or sunday!