Tax strategy for work vehicle.

I will be getting a vehicle allowance as a part of my job. The car allowance will be taxed as ordinary income to me. I travel to a different location for work and my company pays for the flight and the hotel stay at the job site. Now since they are providing me with a car allowance, what is the best way to get a tax write-off. If I rent a vehicle from the airport, can I write off the whole rental, gas and insurance? Or is it better to buy a dedicated vehicle (or lease it) and then I can write off the gas, insurance and vehicle amount. I appreciate you all taking the time to respond.