I've found that my kids are always fascinated with the plane, in general! The drink cart, the window, some snacks I packed. My kids are 5, 6 and 6 and this time when we fly I've made up fun bags for them with coloring books, new markers, new mp3 player, and I made up activity books for them (dot to dots, mazes, etc. - all free printables.) Also, we're flying JetBlue and each seat has their own little TV with a few kids' channels. My kids will be out of control with excitement when they see that. For my daughter (6) I've also packed some Polly Pockets and for my sons (5 and 6) I found two little handheld computer games (SpongeBob Yahtzee and Battleship) for $2.49 each at Target's clearance!
We're in NJ so the flight is just over 2 hours and pretty do-able. Maybe some Floam, paper dolls, pipe cleaners, stickers and a notepad to stick them all on to. My biggest concern is always the delay in the airport and entertaining them there! But then again, they're old enough now that I can bribe them with ice cream adn Burger King if they use decent behavior!