A rental car is a huge convenience over having to wait for public transportation or paying for a taxi any time you need to travel farther than walking distance. But hidden costs can put a crimp in your wallet if you're not aware of them. This list will help you go in prepared.

1. Your Credit Card May Provide an Insurance Policy

When you rent a car, you'll be offered expensive rental car insurance to cover any damages. This can cost upwards of $10 to $25 per day, and you may not need it, even if your auto insurance doesn't cover rental cars. Many major credit cards provide insurance on car rentals at no additional cost. But be sure before you bank on it. Some credit cards limit coverage, while others offer none at all. Call and check first. You may be able to save on the additional cost of rental insurance.

2. But Credit Cards May Not Cover Everything

When you call to check your credit card's policy on rental cars, ask specifically what they cover. Some credit card companies may cover any damages you incur on the rental car, but will not pay fees assessed by the rental car company. These fees can add up.

3. Every Driver Counts and Costs

Even if all your drivers are over the age of 25, you will likely pay a fee for each additional driver registered when you rent the car. Think carefully about how many drivers you need. Designate one or two to keep from incurring additional fees.

4. Youth Drivers Cost Even More

For a long time, rental car companies wouldn't even allow drivers under 21. Now, most do, but a hefty fee can be part of the young driver's experienceusually, a daily fee for putting a young driver (under 25) on the registration.

5. Stick to the Paved Roads

It's easy to miss some of the details rattled off when the rental car representative walks you through the company's policies. There's one you'll definitely want to note: most companies prohibit the use of their cars on unpaved roads. If you do purchase a collision damage waiver or other rental car insurance, this will most likely be voided if you drive on gravel or an unpaved road. Stick to the beaten track, unless you want to pay for your off-road adventures.

6. Fill Up the Tank Before Returning the Vehicle

One stop is essential on your way to return your rental car, and that's the local gas station. Most rental companies require a full tank when you return the car. Fail to do this and you'll get charged for a fill-up. And rental car companies charge significantly more for gas than local gas rates.

7. Avoid the Extra Airport Fee

If you rent a car at the airport terminal, you'll be assessed a surcharge for an airport fee. Rental car companies pay these surcharges to the airport and pass them along to the consumer, so there's no way of avoiding the fee if you rent at the airport. You can, however, hop a shuttle and rent a car outside of the airport.

8. Save Money by Bringing Your Own Extras

It's the little things in life that count, and that's true for rental cars. Need a child seat or a GPS system? Want to listen to the radio? Equip yourself and save big. You could easily pay $3 per day for satellite radio, and daily fees higher than that for a child safety seat or GPS system. Pack your own traveling extras and be sure to have the rental company remove theirsfrom the car and the billbefore you drive off the lot.

The Bottom Line

You can enjoy the convenience of having a rental car, without racking up unexpected fees, if you go in prepared. Do a little research and ask plenty of questions, so you know exactly what you're gettingand what you're paying forwith your rental car.