I used those formula containers, that have the 3 compartments and the swivel lid, for taking formula on the plane. I took 2, so enough for 6 bottles - plus some extra and the scoop in a container, just in case.
I got DS used to drinking his formula at room temperature, so we did not have to get it heated (had a bad experience on a domestic flight when a flight attendant brought the bottle back to me at nearly boiling point). I made the bottles with bottled water that we purchased once we had cleared customs. Bottled water was also available onboard. Once the bottle was finished, I gave it to the flight attendant to rinse out. I only took 2 bottles.
Formula in the US was more expensive than the formula here, and there were no familiar brands, so I would take enough for your whole trip.
For food on the plane, I used the sachets (Rafferty's Gardens??). I also took heaps of disposable bibs (once you get there, have a look for Pampers bibs in the supermarkets, much cheaper than the ones we can get here).
From memory, the nappies/diaper boxes did not have the kg weight on them, so take note of babies weight in lbs. If you like Huggies, there are 2 different sorts. The more expensive Huggies are like ours, the cheaper ones are more like Snugglers.
On V Australia, the toilets at the back of the plane are bigger and much easier to use for changing nappies.
Baby Care Centres at WDW are fabulous. They sell anything you could ever need for baby (we had to buy nappy rash cream).
