I put my puppy policy, which includes things like when the puppy is ready -- why eight weeks, socialization, spay/neuter pros and cons, what is included -- puppy policy, pedigrees, registration application, contract, bill of sale, vet certificate.
A page on training.
Odds and Ends -- what to expect from a new puppy, feeding, grooming, etc.
Then I add some pages from the AKC, Common Household hazzards/poisons, Types of AKC events with a description of each, A page to fill out and leave in the car in the case of emergencies with numbers of people to call, and the dog's vet, and any health concerns.
I was putting in a page of business cards, and had loaded it with cards from my vet, trainer, groomers, emergency vet, etc. and my own card, so that the owners would put cards of their vet, er in there and would always have all the numbers they need right there in their dog's binder.
I use a regular 3 prong 1/2 inch binder, with clear panel over the front, and usually put a picture of the pup in the front. It is the pup's book and all of its papers, contract, everything is kept it one place.
I keep the same book/binder for each of my dogs, and add training certificates and titles into it as they acquire them.
In the front pocket I put the vet/vaccination certification, and usually a pamphlet/booklet by Patricia McConnel, How to be the Leader of the Pack - Dog Training Books at Patricia McConnell
It is just a small little booklet that gives some basic advice for starting off on the right foot.