I know you aren't supposed to double post but maybe you might get better responses in the Travel With Children forum. Perhaps the moderator could move this question?
It would help to know how old your baby is, whether you are travelling with him/her as a lap child or in its own seat.
You will find the Air New Zealand crew to be great with children. You can ring ahead to request a bassinette but it isn't guaranteed until check in. I don't think you'll have any problems with heating food or bottles.
As far as tips go - of course it depends on the age of your wee one, but definitely breast or bottle feed on take off and landing - or else get them to suck on a pacifier, finger etc. Take plenty of entertainment for them. Before we travel I go to a cheap toy shop and buy some 'throw away' toys. It doesn't matter if they get lost on the trip but they are new so there is a novelty factor. Books are always great too. The best tip I could give is don't expect them to sleep just because it is their bed time at home. First time we travelled with our wee man I expected him to go to sleep and got pretty stressed when he didn't! He did eventually but the more stressed I got I think the less inclined he was to sleep!
A previous poster mentioned 'sleepy drugs.' I've never done it but know of people who have. My tip would be if that was something you were keen to do then trial the drugs before you go. I've heard horror stories of some of these drugs having the opposite effect and of kids bouncing off the walls of aeroplanes because the drugs made them hyper instead of sleepy!!
Just relax and enjoy the flight as much as possible. It won't be like any flight you've taken before!! Good luck.