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What's the ultimate sky-high perk? For economy-class passengers, that would be a tray table that doesn't flop open by itself. But most travelers in economy, especially on long flights, would love a horizontal seat.

In fact, Toulouse, France-based Airbus announced at London's annual Business Travel Show last week that it is working on plans to fit bunk beds into economy class. While this innovation may not materialize for several years, there are some perks that passengers--from economy to first class--should be taking advantage of in the here and now.

Granted, it's easy to forget that some carriers are still offering value-added incentives, especially considering that passengers must now pay $7 for a blanket on Jet Blue or US Airways, and part with $15 to check a bag on American or United Airlines. And, of course, most of the perks are available only to business and first-class fliers.

In Depth: How To Score Secret Airline Perks

But there are some nice incentives for everyone, depending on the airline. Air France, for example, offers every guest on every flight a bubbly pick-me-up: complimentary champagne. And yes, it's the real stuff, from the Champagne region of France.

Small Price, Nice Perk
And while most food in economy class now costs more than a wink and a smile at the stewardess, there are some benefits to paying for your meal. Certain airlines, such as Delta, have upgraded their offerings. Instead of an unhealthy, soggy mini-pizza or a mere bag of peanuts, passengers can fork over $8 and get a southwestern Caesar salad created by celebrity chef Todd English.

Life-altering choices? Definitely not. But paying a little extra gets a lot more when it comes to food in economy class. If this still isn't enough, however, and you desperately desire an upgrade, there are ways--other than begging nicely--to move up.

Steven Frischling, a professional photographer who became a travel consultant to C-level executives in 2005, says that for those looking to jump to business or first class, Y-Ups and Q-Ups--known as Z-fares in Europe and Asia--are a better way to go than hoarding frequent-flier miles for years on end.

Y-Ups are special codes on first-class airfare that indicate that the seat can be assigned to those looking to upgrade from economy. To find one of these fares, go to your preferred airline's Web site. Search the first-class seats on the flight you want to take. If any of those seats are tagged to a code like Q***UP, write down that code. Then, search for an upgradeable coach seat (some airlines don't allow upgrades for super-cheap coach fares), and write down the code for that seat, too. Finally, call the airline--they'll usually waive the telephone service fee for frequent fliers, if you ask--and use both codes to request that your coach seat be upgraded to the first-class seat. For the price of coach, of course.

Go Foreign
Sure, this perk does take some legwork, but it's worthwhile on a long international flight. However, Frischling says that the biggest perk is membership in an international frequent-flier program.

"Your best bet is not to join a U.S. frequent-flier program," says Frischling, who left his U.S. programs in 2006 for British Midland Airways' (BMI) Diamond Club.

BMI is part of the Star Alliance, a group of 25 airlines that work together (United, Lufthansa, Air Canada and Air New Zealand among them), which means your points and upgrades can be applied to any of those airlines. While most U.S. airlines do not offer complimentary lounge access to frequent fliers, most foreign carriers do, which means you get the benefit of using those facilities within the U.S.--on airlines like United--without actually belonging to their frequent-flier programs.

Along with BMI, Frischling says that Air France and Korea Air offer the best perks (Continental is a partner of the latter). For example, once you've flown 100,000 miles on Korea Air, you're automatically given platinum status for life, which includes access to hotels discounts, rental car services and even bonus flight tickets.

While foreign carriers take extra care of frequent customers, it doesn't look like perks on U.S. airlines are going to improve anytime soon. In fact, they may get worse. Richard Laermer, a marketing expert who travels the world promoting his books on the topic, including last year's 2011: Trendspotting, uses the tactics such as the aforementioned Y-Ups, to score deals.

"Perks are dropping like flies," says Laermer. "I spend all my time these days figuring out what's being offered."

But perks are still available for now. So while it may take some legwork, from the simple (edible food), to the more complicated (first-class upgrades at economy prices), there are hidden perks out there. You just have to know where to look.

In Depth: How To Score Secret Airline Perks