there are a number of threads on this...Singapore airlines are brilliant if you are flying them. We did this in April with dd when she was 8 mths old. We had night flights and simply put dd into her sleeping bag and off she went.
Pack layers so that you can add or take off as needed. Temperature can be quite warm still during the middle of the day but cold evening and morning - but that depends on where you are. Still take sunscreen - handy wipes pack to have if you need them. We found them very helpful with dd.
Singapore airlines provided us with a couple of nappies, bib, wipes etc. I simply took a days worth of formula ( in premix cartons), steri bottles - jettison on the way, nappies, wipes etc. But she basically slept the whole way. We only had an hour and a half on the ground.
try to prebook and have the sky cot confirmed - the only thing is during turbulence you have to take them out of the cot.
The flight crew were very good in helping if you needed help with the baby. The even took someone else's baby for a wander round the cabin as they were having trouble settling.
Our dd adjusted quite quickly to the change of time and although she had some jetlag she was fine. We spent three weeks there. You just have to go with the flow on this we found.
On take off we just had a bottle of water for her to drink. Gave it to her as we left the ground.
There are a number of threads on long haul flights with babies - I am sure I did a search via google and got lots of handy hints too.
here
here
here
here
here
hope that helps