2. Stock up on a bunch of cheap, small toys. Unpack from their boxes and repack in ziploc baggies. You will be surprised how little space they will take up once they're out of the packaging. Hide them from the kids and produce one every hour or so. I find little figurine sets like playmobil, or disney character playsets great. Lego also make some small sets (Harry Potter etc). The downside is that these sets usually consist of a ton of little small pieces so you'll be spending some time crouched down picking up the bits from under the seat in front
3. Playdoh have some great little small tubs with tools on the end. Buy one or two of these, spread a newspaper under the seat and let her enjoy. Downside is that you may end up with playdoh on your clothes
4. Print a bunch of coloring pages off your kid's favourite sites. A google search usually yields a ton of stuff and unlike coloring books, you can bin them with trash before you get off the plane. Sticker and decal books pack light and will also burn up 20 mins or so. Try to find some novelty crayons (we bought a great pack of crayons shaped as Disney characters last year) to interest her.
5. Buy a small notebook of colored paper, a glue stick, some glitter pens, some confetti or paper shapes and some fluffy stuff (check out any craft shop). OK, she'll make a bit of a mess, but she'll be happy (the FA's are really going to love you). This stuff will all pack up pretty small in some baggies and can also be left in the trash. I have yet to meet a kid who doesn't love sticking stuff onto paper.