We stayed with Thomson all Inc (buffet service) when dd was 14 months. Breakfast was easy as pastries, cereals and yoghurts were fine for her, however, she was a very early riser (usually 5 am) so I packed a few porridge, yoghurt and fruit pouches (Ella etc) for her to have when she first woke up and to have as a snack in the afternoon. We also popped to a supermarket and grabbed some fruit and yoghurts to keep in the fridge in our room.
Lunch and dinners were again fine, plenty of food to choose from although she mainly ate pasta, rice and soups. The salt content is an issue but it was only one weeks worth of food and there will be fruit and water available to somewhat mitigate it.
Contrary to pp, 9 months would be a good time to travel as its unlikely your dc will be walking. You can buy calpol sachets which are useful for the flight.
If I remember correctly I don't think under 2s does get hold luggage. However, Thomson hold luggage is quite generous, we didn't need a specific bag for dd, we had enough room between mine and dp's rucksacks for all her paraphernalia. In any event, I wouldn't want to deal with a trunki for a 9 month old given you'll presumably have pushchair (you can keep pushchair with you right up to getting on the plane) and your own hold luggage to deal with (I wouldn't even entertain one now for my 2.5 year old)
I can't help remember formula I'm afraid.