Harriet Baskas Travel writer

How much do you really need to take with you when you head to the airport? Think — and pack — carefully, because these days an extra bag or two can cost you big bucks.

Earlier this month, United Airlines announced a significant and, to many, an alarming change in its checked baggage policy. Every domestic passenger will still be entitled to check one bag weighing up to 50 pounds for free. After May 5, though, it will cost $25 (each way) to check a second bag — that is unless you've purchased a refundable (and more expensive) ticket or hold Premier status or above in the airline's Mileage Plus program.

US Airways on Tuesday became the first legacy carrier to follow suit, announcing a $25 charge of its own for a second bag.

Ka-Ching!
Don't mind paying that $25 and want to check more than two suitcases? Get ready to empty your wallet: Come May, United will begin charging an additional $100 for each bag beyond two that you want to check. It doesn't stop there: the carrier is rolling out other changes to its bag check policies, but the bottom line is that soon the more you tote the more you'll pay.

Travelers are pretty much up in arms about all of this. In fact, as of last weekend, more than 1,500 people posted comments about the move on the   msnbc.com message boards. A few folks are optimistic and hope that the new fees will encourage others to pack light. (Don’t hold your breath.) Others predict a sharp increase in the size and number of carry-on bags other passengers (it’s always other passengers) will try to take onboard with them. But most responses are along the lines of the "here we go again" comment that Parrot4 posted: "... I love to fly for the convenience but that 'convenience' is slowly becoming inconvenient. More fees, higher prices, more waits, more cancellations, etc. For a family of 4, it's cheaper to drive again, even at $3.00 a gallon."

No way out?
If you don't like United's new bag-check policy, of course, you can choose to fly on another airline that doesn't levy a fee for an extra checked bag. But experts who study these things say don't count on that workaround being available for much longer. United Airlines estimates that it will generate more than $100 million a year in new revenue from this move, so other major U.S. airlines will surely follow suit.

Charging for checking bags is nothing new. Several budget carriers in Europe and Canada do this, as do some smaller carriers in the U.S., most notably Spirit and Skybus Airlines. In fact, blaming it on the increased price of fuel, discount carrier Spirit Airlines recently announced that its fees for checked items have increased from $5 to $10 when reserved online. Passengers who first request to check baggage when they arrive at the airport will now be charged $20 per bag (up from $10). ("Yeah, so pack smartly," the airline advises on its Web site.)  And word has it that Skybus Airlines will now charge $12 — up from $5 — for the first two bags a passenger checks. (For now the airline’s $50 fee for additional bags beyond two remains unchanged.) The news isn't all bad. For those who wish to save a few bucks, Skybus is offering a $2 discount to travelers who print their own baggage labels at home and who check their bags in online at least 24 hours before departure.

What can you do?
So how can a well-mannered traveler be suitcase savvy and avoid having to pay to check that first or second bag? Here are a few ideas:

Pack prudently 
There are plenty of folks who can go away for a week or a month with all they need folded neatly in a carry-on. Others can't leave home for an afternoon without an overstuffed suitcase.

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The truth is that most of us over-pack. I rarely check a bag and pride myself on packing light. Yet, I have a perfectly lovely pair of pants and a dressy skirt that I've taken around the world in my carry-on and never worn. And although I feel prepared for just about anything with my assortment of travel gadgets, I rarely use them. They just come along for the ride.

But why pay to check a bag full of items you may not really need? Before your next trip, take a moment to read one of the many Web sites, books or magazine articles that offer packing tips. You'll learn a trick or two for lightening your load, creating a travel wardrobe of mix and match outfits, and for getting your stuff from here to there with fewer wrinkles. You may discover that you can leave that second suitcase behind and do just fine.

Carry-on what you can
Most airlines request that each passenger board with just one bag that fits either under the seat in front of you or in an overhead bin, plus one small "personal item." We've all seen people board airplanes with much, much more than that. And the definition of "personal item" gets stretched pretty far. ("Actually this kitchen sink is my briefcase.")

While it wouldn't be very well-mannered of me to (officially) encourage you to ignore the rules of your airline, I'll urge you to check your airline’s Web site for the acceptable dimensions for carry-ons — then get out your tape measure and see if you can legally "up-size" your suitcase.

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