Fly when your kid is tired: If possible, schedule your flights around your kid's nap time, or fly in the evening when she'll be more tired. (Beware: You also could end up with a tired, cranky kid who can't sleep on the plane.)
Collapsible umbrella stroller: A stroller bag is a good idea, too, if you're at all concerned about the stroller getting dirty or tossed around and broken by burly baggage handlers.
Change your toddler just before boarding: This will, hopefully, help delay your first trip to the plane bathroom for a diaper change.
Keep diapers and wipes handy: As soon as you board, put wipes and a few diapers in a seat pocket. It'll be easier to have those items accessible when you need them.
Take your car seat: The safest way for toddler to fly is in a car seat. Check on discount on fares for kids under 2. You also may want to invest in a car seat backpack which allows you to transport the seat through the airport more easily.
Dress in distinctive clothes: Time to break out the neon hats or T-shirts! Yes, you will look geeky wearing all the same color shirt, but it's better than losing each other in the airport, right?
If you're really worried about a toddler walking off and getting lost, buy a child harness: Kid leashes may seem harsh, but they're not nearly as harsh as the panic you'll feel if you lose track of him.
Portable DVD player or video game player: Even if your flight has a movie, your toddler may not be able to see the screen or he may be disinterested in or be scared of the airline's film. Let preschoolers go nuts with portable game consoles, like a GameBoy or Leapster®. Make sure to charge them before you leave and bring power cords or extra batteries.
Bring a goody bag of toys, books and games: For maximum entertainment value, introduce the goodies one at a time.
Let your kid have the window seat: Toddlers and preschoolers usually love looking out the window and seeing the clouds—not to mention the airport workers loading the luggage.
If you know your kid(s) will be noisy, book seats in the back of the aircraft, where engine noise will help muffle screams.
Request the bulkhead for more room.
Pre-board: Most airlines let people traveling with small children get on the plane first. Do it! It's easier to stash your bags and get settled, and you won't get stuck standing in the aisle holding mountains of stuff. Getting off the plane last is also a good idea.
Leave extra time for everything: Getting to the airport, checking in, making connections, etc.
Pack snacks: This is one of those times to indulge kids and let them have a bit of junk food (without encouraging a sugar high, of course). Remember: Hungry equals cranky, so do what you can to avoid it.
Bring several plastic zipper locks bags: Great for wet, messy clothesthe kids' and yours.
Carry on an extra outfit for yourself: You never know just how messed up your clothes will get. Also try to dress in layers, so you can peel off tops as they get dirty.
Offer to buy a drink for the people sitting immediately around you: It's a great way to buy some goodwill. You could also bring a few sets of earplugs and pass them out before takeoff. Apology cards are great for the end of a bad trip, too.