I have just returned from Bali with a very active 19 month old. The flight was 6.5 hours so a longish one. We packed heaps of snacks, a magna doodle (not sure how its spelt) you can get travel size ones at Target, small toys, books, his dummy and blankie, crayons and a colouring book. Our salvation was my husband downloaded my sons favourite tv show to his iPhone and this worked brilliantly! Also we let him wander up and down the aisle.

As EmLuLu said expect the worst and you maybe FX surprised.