In today's U.S. airline fare wars, base ticket prices may be on the decline in some cases. But carriers are making up for it by charging extra for services and conveniences that used to be customary. Read on to learn more about these additional charges and how business travelers can keep an eye on the bottom line.

At the Airport
In 2008, the Transportation Security Administration is expanding its Registered Traveler program. Once an applicant is approved, benefits are expected to include reduced wait times and/or dedicated security lines, a concierge service for luggage, parking privileges, and discounts for services and concessions. The program is available at the discretion of each airport authority.

Baggage
The convenience of checking your bags curbside and avoiding long lines in the airport will now cost $2 per bag at some major U.S. airports. Just checking bags also now costs money with some carriers. Spirit Airlines charges $10 each for the first two checked bags or $5 if you pay via the company's website. The cost is $100 per additional bag. Go over the standard 50-pound weight limit and fees will range from $25 to $150 per bag.

If you don't want to hassle with luggage at the airport, Luggage Free and Luggage Forward are two of the new companies that provide luggage shipping service. The cost depends on the number of bags and when you need them to arrive. The price ranges from $1.65 to $4.40 per pound each way. While this may seem expensive, you won't have to check or pick up your baggage, and your luggage is less likely to get lost. If you have extra time and don't need the door-to-door service, you can save money by shipping your luggage through FedEx or UPS.

At airports, convention centers, hotels and cruise ships, Bags, Inc. offers a remote check-in service for you and your luggage. You can hop on a bus and go straight to security at the airport. More U.S. locations are in the works for 2008.

Boarding the Plane
Some carriers, such as SkyBus, now charge $10 to $20 to board the plane before anyone else. If you have carry-on luggage, the additional cost may be worth it to claim overhead space. On Southwest Airlines, if you purchase a business select fare, you get to board first in the "A" group.

Food
There's a good chance you'll be charged for food once onboard, but at least the choices and quality are increasing. Carriers are hiring gourmet chefs to plan and design their menus, which is a far cry from the gelatinous turkey sandwich on white bread you used to receive. For example, Delta has new signature entrees from celebrity chef Todd English that include a roast beef steak Cobb sandwich and grilled Mediterranean shrimp salad.

Other carriers are offering snack items a la carte. On Spirit flights, water is free, but a soft drink will cost you $1 and a bag of chips $4. And you better have a credit card, since Spirit doesn't allow cash purchases onboard any of their aircrafts. The low-cost and more reliable option is to bring your own food.

Entertainment
Want to watch a movie onboard a flight? While some carriers still show complimentary movies on longer flights, they're diminishing quickly. Most major carriers are installing video-on-demand systems that allow passengers to choose a movie or video to watch on their own seatback monitor for $6 to $10 each. Be sure to bring your own headset to listen, as these will set you back between $2 and $5.

Wi-Fi
Finally! Southwest Airlines, JetBlue and Virgin America will be equipping their planes with Wi-Fi in 2008 to provide broadband internet connectivity to passengers. Other carriers, such as American Airlines, are also looking at adding this service.

The U.S. airline traveler has been relatively spoiled until now. European carriers have been charging for these "extras" for years. Now that those same low-cost European airlines are entering the U.S. market, American-based carriers are watching carefully to see how consumers will react to these additional charges. One thing's for sure though: Carriers will continue to push the limits on what passengers are willing to pay for.