Having a rental car can give you a huge advantage over having to wait for public transportation or having to pay for a taxi every time you want to go somewhere not within walking distance. But the hidden costs can come back and get you 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 an expensive option at the counter of purchasing rental car insurance to cover any damages. This rental car insurance is usually rather pricey - from $10 to $25 per day - and you may not need it, even if your auto insurance doesn't cover rental cars. Many major credit card companies, if used for the car rental, provide coverage to the cardholder with no additional cost. But be sure before you bank on it. Some credit cards may limit their coverage, and not all credit card companies offer it. Call and check first, and you may be able to save on the additional cost of rental insurance.

2. ...But It May Not Cover Everything

When you do call to check your credit card's policy on covering rental car costs, ask specifically what they cover. Some credit card companies may cover any damages you incur on the rental car, but will not cover the cost of fees assessed by the rental car company. Fees can add up, too, so you don't want to be left holding the bill.

3. Every Driver Counts -- and Costs

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

4. ...And Youth Drivers Cost Even More

Or yourself, if you're under 25. Age is not an advantage for rental car drivers. 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 experience -- usually, a daily fee assessed for putting a young driver (under 25) on the registration, whether or not they actually do all of the driving or even drive every day.

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 policies. There's one you'll definitely want to note, and that is that most companies prohibit the use of their cars on unpaved roads. If you do purchase a collision damage waiver or other rental car insurance, it will most likely be voided when you drive the car on gravel, or an otherwise unpaved, road. So stick to the beaten track, unless you want to pay for your off-road adventures.

6. Save on Gas by Filling up Before Returning the Vehicle

One stop is essential on your way back to return your rental car, and that's the local gas station. Most rental car companies stipulate that you return the car with a full tank, and if you don't, you'll get charged for the gas you didn't put in the car at rental car rates. And rental car companies often charge significantly more for gas than local gas rates.

7. Avoid the Extra Airport Fee

If you're traveling by air, and you rent a car from the local counter at the airport terminal, you'll get a surcharge for an airport fee. Rental car companies are legally obligated to collect and pay these surcharges to the airport, so there's no way of avoiding it if you rent at the airport. You can avoid it by grabbing a shuttle to your hotel or to a downtown area and renting your car there.

8. Save Money by Bringing Your Own Extras

It's the little things in life that count, isn't it, and that's true for rental cars and the associated fees. 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 fees higher than that for the daily use of a child safety seat or GPS system. Whenever possible, pack your own traveling extras and be sure to have the rental company remove theirs - from the car and the bill - before 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. The best tip of all is to do a little research and ask plenty of questions, so you know exactly what you're getting - and what you're paying for - with your rental car.