On a long flight problems on the plane are largely space related. Most airlines provide a cot or carseat type seat (BA) for babies to sleep in - however, only very young babies will fit into the cot. Not all babies will sleep in the carseat & only BA provide them I think. The size of the cots differ slightly from airline to airline, and the level of comfort/security also varies. The BA cot is relatively short. Also there's no point putting a baby who can sit up in a cot, as they're likely to fall out if you are asleep. There should be some kind of strap or seat belt option perhaps.
Babies under 2 fly free (or for a small charge), but once they are 2, you must buy them a seat. If they're under 2 but too big for a cot & there's no carseat option, then they're on your lap THE WHOLE TIME.
If you want to make some serious cash - please invent some kind of comfortable sling thing that you can wear when sitting down in a plane seat so that your baby is attached to you/sleeping on you, without you physically holding them. These do exist, but not sure whether they are any good.
If you're breastfeeding you escape the problems of storing/carrying/heating up milk - but the stewards will heat up bottles (they typically overheat them). Security is a hassle when travelling with pre-made cartons of formula or baby food. I have been told I have to open HALF of all the different kinds of food/formula - which not only means waste, but if you don't anticipate it, you will run short on the flight. Once you've opened it, you can't store it - so you have to throw it out.
Changing baby on a flight is unpleasant - there's little room in the loos as you know, but it's not impossible.
Carrying essentials? Well, I carry my nappy bag - overloaded with stuff - a backpack would be better.