The following are precautions you can take to protect your car and its contents:
Before reaching your destination, everything you want to leave in your car should be already be packed away and hidden.
Park in airport lots or garages, whenever possible, in view of the exit toll booths or parking offices. Increased traffic discourages potential thieves.
Always park with your car's trunk facing out where more people will be able to see if someone was trying to break into your trunk.
Your car is less likely to be broken into if you park in a garage. Remember to remove or lock up items most attractive to potential thieves, including GPS units, accessories to a cell phone or MP3 player, or an E-Z Pass unit.
Whenever possible self park when leaving your car in a garage.
Steering wheel locks or blinking alarm systems often inspire thieves to leave cars with such devices alone.
Neat cars are less liked to be robbed because a thief does not think that things of value are covered by jackets or towels strewn about. Similarly, power cords left in sight in parked cars can lead thieves to believe electronic devices may also be in the car.
Always confirm your valuables are still there when you return to your car. This is important when filing a police/insurance report.
The type of car you rent can impact the likelihood of you getting robbed:
Rent cars that are not easily broken into and have trunks large enough to store what you will be carrying.
The more basic and nondescript you car rental is, the less likely it is to attract unwarranted attention.
Never leave the rental contract in the car since this has the information you will need if the car is stolen.