Already made formule, you can bring what you need for the day because they know that delays do happen. Diaper bag can be brought in the airplane on top of your carry on. To save you aggrevation and to be able to bring more formula then needed, you can always bring your powder formula in a container and after security by a few bottles of water to take with you. THat what I did when I travelled with our triplets at the age of one other wise I would have had way to much weight on my shoulder from all the bottles LOL