Familiar blankets, pacifiers, stuffed animals and other comfort items can be essential tools for calming down a frustrated child. Bring backups in case you lose one or it gets left behind. You don't want a temper tantrum on the plane because a blanket was left at the gate.
Even if your kids doesn't need a favorite toy or other familiar item, pack a travel blanket and pillow to help them get as warm and comfortable as possible in their seats. Also, come prepared with some infant pain reliever, in case of ear pain or other discomfort.