Should you pay the collision insurance when you rent a car? Collision insurance will add $10 - $20 per day to your car rental; do you need it? Generally not. If you have collision coverage on your own car, your policy will probably cover you for any collision damage while driving the rental car.
(Check with your agent, and if you're traveling outside of the US, ask if coverage applies in the country you are going to.) Also, many credit cards provide collision damage coverage if you use that credit card to rent the car. (It seems like most cards cover all countries except Jamaica and Ireland - north or south)