I did uk to Oz with a 2 yr old. I wrapped up lots of little presents (cheap £1 shop things) and brought one out every few hours when it looked like things were getting a bit tricky. Seem to deflect tired-related tantrums
Suggestions: take a bottle (sports style, not teated, unless thats what they are used to), and fill it with a prefered drink when past customs (we bought a pint of milk, which was OK for the 12 hrs without a fridge), take loads of snacks - they will sometimes want food at inconvienent times, take sticker books, makes sure anything you take doesn't stop working if you loose one small piece!
Lots of adults were walking round with small children - the kitchens at the back of the plane seemed to be the gathering place!
We had bulk head going out, and DS was small enough to be offered a bassinet at 20 mths (!), he was pretty dinky tho.
Coming back, we had normal seats (bought him one, even tho we didn't have to), and put armrest up, and he slept with his head on my lap.
Sachets of calop were our saviour coming home - it was the only think that stopped him screeming, so I assume he really was in pain.
Have done this flight with dd on my own many times as lived in Sydney. Have flown business alot which helps as can lie flat but have done economy too. My dd is 7 now but been flying since a baby, to be honest most flights she sleeps right through, not even waking for dinner. Personally i dont bother with dvd players or ipads, dont know who you flying with but emirates for example has over 500 films and pretty much every kids channel and most disney films etc which you can stop/start when you want.
We put arm rest up and daughter puts legs on me and sleeps. Soon as we board and before take off we go to the toilet and change into PJS (yes i do this too lol, i have to be comfy!)
I'm about to go alone with my 2yo DS to Sydney and I'm already having sleepless nights about the flight!! Have already downloaded a ton of apps and movies onto our iPad - but ANY OTHER TIPS about flying with a toddler would be greedily received. Howwwww do they sleep in a chair? Should I choose bulkhead where there's more space - or a normal seat where you can put the arm rest down?? Anyway, any advice from veterans of long-haul air travel with littlies would be gratefully received.