Your carry-on bag is your most precious possession when traveling. It contains your identification and tickets, but it can also save you from boredom on a long flight and from wearing the same outfit day after day if your checked bag gets lost.

Which bag is best?

Before you start packing, measure the bag you want to use. There are no TSA or FAA regulations that state exactly how big your carry-on can be, but the general rule is that it must fit under your seat or in the overhead compartment.

The exact guidelines vary from airline to airline and the TSA urges you to contact your airline before you fly. With United Airlines, the maximum size is 9 inches x 14 inches x 22 inches (22 cm x 35 cm x 56 cm), while American Airlines has a limit of 18 x 14 x 8 inches (45 x 35 x 20 cm). Check your carrier's website for the exact maximum dimensions before you get to the airport. 

If you're bringing a laptop or tablet on board with you, your carry-on bag will ideally have with a padded compartment to protect them. Be sure that these compartments are easily accessible during security checkpoints since the TSA will require you to remove your devices and you won't want to be struggling to get them out while also dumping everything else into a plastic x-ray tray.

Another important factor is comfort. You'll be carrying (or rolling) this bag through security and down long corridors, or perhaps running with it to the gate so you don't miss your connection. Do you need padded handles or cushioned straps? Make sure your bag fits your comfort needs.

Pack smart

While packing, be sure the things you'll use the least are on the bottom of the bag, while more useful items are on top.

It's a good idea to keep most of your valuables in your carry-on, just in case your bags are lost. Be sure to pack jewelry at the bottom of your bag, away from the opening, and keep your wallet in an inner pocket so they will be harder to steal. 

You may also want to keep a few bills hidden in the pages of a paperback or magazine you brought with you. Most thieves won't think to steal reading material, so you'll still have some cash even if your wallet is snatched. Another good hiding place for some extra cash or a traveler's check is between your phone and its case.

Two more things that should always be in your carry-on bag, not your checked bag, are prescriptions and contact lenses or glasses. If your checked luggage gets lost, it can be hard to quickly replace medication and even harder to get replacement prescription glasses or contacts.

Airports tend to lose luggage sometimes. It happens. It's important to pack a spare set of clothes (and underwear!) in your carry-on to hold you over until your bags are found. Pack lightweight clothing that can be rolled up and put in the bottom of your bag without wrinkle worries. Fast drying clothes are also a good idea, just in case you'll need to hand wash them in the hotel room sink.  

What to do with your gadgets

Whether you're planning to get work done or looking to stay entertained, your laptop or tablet can be your most important item in your carry on – be sure you use it right.

Airplane mode

Remember, airplane mode is called airplane mode for a reason – the flight crew will ask you to use it when the airplane doors are closed and during your entire flight. Use it on your tablet, phone or laptop when asked to. Jason Cipriani has a great post on how and when to use Airplane Mode on iPhone.

Stay charged

On a long flight, your laptop, phone or tablet can quickly go from 100 percent charged to desperate for power, especially if they are your main source of entertainment. Be sure to bring a charging pack to combat low-battery fears. If I have a window seat I prefer a solar charger, like the X-Dragon Solar Charger Power Bank or the Beartwo Portable Solar Charger, because the sunlight coming through the window means it never runs out of power. Traditional battery packs, such as the Mophie Powerstation or the Anker PowerCore, are also good choices no matter your seat assignment. Both are small, but carry a decent charge.

Pack the right headphones

Now that your power concerns are covered, think about your ears. Many airlines supply free headphones, but the sound is less than spectacular and they can be flimsy. Sound-canceling headphones are ideal companions for your carry-on. You can use them to tune out crying children or talkative seatmates, even if you're not listening to music. Here is our list of best noise-canceling headphones for 2018.

Need ideas of what to do with your devices while in flight? Mike Sorrentino has a great article with 5 steps to make your phone or tablet an in-flight entertainment center.