1. Kitten milk replacer - you can buy this at the pet store or even at your local Wal-Mart. This is so handy to have on hand in case a young kitten comes into your care. I have also found it very useful for older cats who look a little dehydrated and just need a boost. Be SURE you have a syringe or bottle to administer it if need be.
2. Flea and tick drops - I use Frontline Plus. You can bet that if a stray cat or kitten comes into your care, they are gonna be covered in all sorts of nasty things - especially fleas and ticks. This will kill 'em dead!
3. Dawn dish soap - This may sound a bit odd, but it has been vet-recommended to me a number of times specifically for kittens. It kills fleas immediately and is especially useful if you have a young kitten come into your care who is too young for the flea and tick drops. Just be careful when you bathe cats and kittens to never make any sudden noises, and use water that is comfortable to your skin, not hot. Always wash all the soap out very well when you are done.
4. Dewormer - And I don't mean those cheap dewormer drops you can buy at the store. I am talking the stuff you get from the vet that kills everything including tape worms, because most stray kittens have them. Be sure to consult with your vet on the safe age to administer dewormer to a kitten.
5. A whole lotta love and patience! Kittens and cats who find themselves without a home may be spooked or untrusting. We have one cat whom we have owned for 4 years now who still won't let us pet her, but she lives right on our front porch. And it is so worth it!! She is so sweet and I am glad she has found a safe haven with us.
Also, it is important if you take a cat or kitten in to get them examined by a vet and spayed or neutered as soon as possible to prevent more stray kittens from happening!!