Tablet

Load it with your child's favorite games and television shows, plus a few new ones. I also bring along an old phone, fully charged, for pretend play.

Headphones

If you're starting to feel your skin crawl at the sound of Elmo's voice, your fellow passengers probably are, too. Bring a pair of headphones for your child, but practice using them ahead of time. (On our first flight, my daughter kept ripping the headphones off and putting them in her mouth.)

Toys and Books

To kill time, wrap them like presents and use lots of tape (but keep the crew in mind and ask for an extra bag for your trash). One mom suggests books with compartments and windows that your child can open and check out.

Art Supplies

Bring crayons and paper, or even a chalkboard for less mess.

Magnetic Blocks or Other Kinetic Toys

Magnetic blocks are ideal on planes, as they're the least likely to fall to the floor.

Diapers, Wipes, and Burp Cloths

Make sure you check that the diaper bag is fully loaded before you head out. In the whirlwind of getting out the door, these basics often get taken for granted. A good tip for those traveling with babies: Put a nighttime diaper on for longer flights—you'll worry less about it leaking.

Change of Clothes

Bring one each for child and parent—when kids spill, parents often get caught in the crossfire. Pack clothing in a ziplock bag in case something spills.

Snacks and Milk

Small cartons of ultra-pasteurized, shelf-stable milk are extra convenient, as they don't need refrigeration. The 3.4-ounce rule about liquids does not apply to baby needs—just offer them up for inspection when you go through security.

Cozy Blanket

The familiarity of whatever your kid snuggles with in bed will keep her comfortable on the plane. A favorite pillow or stuffed animal can also do the trick.

Car Seat

Again, familiarity engenders comfort. Also, according to the flight crew, it's safest for small kids to fly in their own seat. We use a folding luggage cart to wheel ours around the airport.

In-Flight Earplugs

Not just any old earplugs, these are specially designed to help mitigate the pain from changes in air pressure, which is often why kids start wailing during the descent. Practice before the flight so your child gets used to them, or do what I did: sneak them into her ears while she's sleeping.