we flew to Oz 2.5 years ago, with dd1 (then 5, severe ASD) and dd2 (then 2.5).
we flew with Qantas, and they were really great - fantastic helping us with the dds, really helped out with any requests we had, and were fab when a fellow passenger got stroppy with dd1 (a travel agent mix up meant on our second leg we didn't have seats together; fellow passengers wouldn't swap seats - no one in the whole cabin would swap, the stewards were
as it had never happened before. on take off, dd2 (sitting with dh, in front of me and dd1) got upset as she wanted to be with me. dd1 got upset as her sister was upset, and she coudln't see her or help her. the man sitting next ot dd1 got stroppy, and the stewards handled it brilliantly - told him to shut up or leave the cabin, basically, as he had brought it on himself by refusing to swap seats so that a 2 year old could be near her mum)
anyway, enough of that 
we took:
iPad and ipod touch, loaded with apps, dvds etc. sticker books worked for us, but might be a bit young for your two.
foodwise, ask away - I am queen of packing for allergies/fussy diets
. dd1 is gluten and dairy allergic, and there is no airline meal that can be found for her. it is possible to pack for a lengthy flight, and get it all through security.
I use a combination of: thermos flasks (you can get ones which keep stuff hot for up to 7 hours), things that can be eaten cold (pizza, sausages, nuggets) and sandwiches. don't forget the breakfast cereal, either - one of the easiest bits to pack! we have issues with drinks too (dd1 cannot have apple or orange juice, or any fizzy stuff, and won't drink water), and we have had doctor's letters in the past to enable us to take enough liquids thorugh security to last for the flight. same for taking a sports bottle/toddler cup through with liquid in - it can be done, you just need a bit of extra time to explain.
I have also, before now, packed proper sleep cues - so pyjamas, bedtime book, teddy etc, in order to do a 'proper bedtime' to try to get them to settle. it worked well for us, and on the Oz flight we all probably got a good 8 hours sleep across the 2 flights.