Just a few thoughts:
1-Be sure there is nothing visible in your car that might attract a smash-and-grab. This includes empty backpacks and shopping bags that could possibly have something in them.
2-Consider taking garage door remotes into the office with you rather than leaving them in the car. Do not leave house keys in the car.
3-To the extent possible--and it can be difficult with children or other family members at home during the day--keep the door between your garage and home locked.
4-Contact your State legislator about removing your home address and other personal information from the registration that has to be kept in the car. In a day of wireless computer communications there is very little need to have this information printed on a document you have to keep in your car. I should think that vehicle description with VIN number, license plate number, and expiration date is all that is really needed; MAYBE the name of the registered owner.
5-Clean out all other documents from your car that have your name, address, or other personal information on them. This includes letters and bills. Keep the car clean so if it is stolen or broken into, there is less to be taken.
6-If you have a P.O. Box or private mail box somewhere you may consider using that for your vehicle registration rather than a home address.
7-You may give serious thought to investing in a small car safe. I've have one from "Center-of-Mass"...