How exciting! I'm sure you will have an awesome trip. I can't wait to see pictures.
Kat has some great ideas! Here are a few more that worked for us on long (6+ hour flites) with our daughter:
-bring a new toy for the flight; it does not have to be expensive, just something small & new. For my dd, a Dora action figure was perfect when she was smaller. Now I pack a brand new book and coloring book, and a fairy doll of some kind. Yes, it means spending money, but I sort of factor it into the overall trip cost.
-coloring books & crayons in a Ziplock; pencil/pen/notebook for doing things like tic tac toe, etc. We also like hangman, pictionary, mazes, etc.
-new book or magazine to read to them (or older kids can read to themselves, of course!)
-new and old favorite games on your electronic device of choice
-make sure headphones are working and packed (we once goofed and forgot her headphones, so all the movies we'd carefully selected were good for nothing!)
-my child gets constipated on travel -- not sure if that happens to many kids - but I always make sure to bring along some things that are good to help (raisins, apples, mini packs of mandarin oranges, etc.) I always pack some fruit cups and things like that in the checked luggage too, because even though there are stores everywhere, it's good to have something we trust and that she likes ready to go immediately.
I usually end up talking to her a lot - we tell stories together. She likes it when I make up stories.
I always make sure that I have Children's Tylenol or Advil, children's Benadryl, regular aspirin, bandaids, Chapstick, etc. in a big Ziplock in my purse, just in case of emergency. I'm always thinking, "What if we get stuck on the tarmack for like 12 hours, and she gets a horrible virus and a fever, and we have no medicine?" So far we've never needed it on an airplane, but it makes me feel better to pack it! Of course, liquid medicine gets "bomb-sniffed" at the security checkpoint, so I am prepared for that now and know it will take us a bit longer to get through. That freaked me out the first time but now we're used to it.
My dd sometimes gets earaches on the way up and down, so I always pack lollipops and small candies (like a pack of M&M's) to give her. The chewing/sucking seems to help.
I always bring extra drinking straws along in my purse too, and an extra empty sippy cup with a lid (those disposable plastic ones.) That way I can easily let her have access to water or juice on the plane w/out having tons of spills. WE usually buy a bottle of apple juice and a bunch of waters in the airport after we go thru security. Then I can fill her sippy and she can stay hydrated and happy.
Those are my best suggestions!