CRA requires that a log be kept for all expenses related to the claim of the use of the car.

The log should include a daily record of kilometres driven for business use as well as kilometres driven for personal use. Also the names and locations all of the clients visited for business.

Of course you should also keep all the receipts related to the use of the car such as gasoline, car repairs, lease payments (if applicable), car insurance, plates, CAA, parking, and tolls.