Make sure you have something she can chew on or suck on during landing. Pacifiers, bottles, lollipops; I frequently had a baggie of cut up grapes in the diaper bag for my boys. Bring some new small toys that she hasn't seen before. The airline magazines are good entertainment, as well as peanut containers, plastic cups, water bottles - you can always put something in one (a coin for example) because it makes noise when you shake it.
Bring some small snacks (Cheerios, fruit snacks), a sippy cup, and something she'll drink. I frequently had some juice and a bottle of water to water it down.
Something you can use to put under her to change a diaper is good in case you can't go to the bathroom to do it, as well as those disposable diaper baggies (Wal-Mart, Babies R Us, etc.). My backpack diaper bag has a fold-out plastic changing pad with places for diapers, wipes, etc.
If it's during nap time then you could give her a dose of Benedryl prior to help her relax and sleep, as long as it doesn't make her hyper.
If you have to get up the faucets in the bathrooms are fun to play in!
Good luck and remember that you'll probably never see any of the people you travel with again.
Judy