For a more detailed information about vehicle registration, please check out this link.
What are the documents that I need before purchasing a car?
You only need to show your picture ID. It can be a Driver License, a State ID, or a passport. College ID card will not work. This ID is only used to verify your name on your check or credit card. If you buy the car from your friend, you may not need to show anything to him / her.
What documents should I carry with me all the time in my car?
You should carry with you the following documents all the time in you car, otherwise you may be penalised by the traffic cops:
Valid Diver's license
Registration of the vehicle
Copy of the Title of the vehicle
Proof of car insurance (you can use the card sent to you by the car insurance company)