We travel a lot with our 18-month old. He loves to look out the window and watch evertyhing that is going on. Books are good and hand snacks (gold fish, cheerios). One thing that I learned on our last trip is when asking at check in about the food I was bringing (jarred baby food). There happened to be a TSA agent talking to the person checking me in. We asked her. She said whatever was reasonable amount of food for the trip could be brought. Then she said, it really depends who you get when you go through security! Yeek! So, when it comes to baby food and related items it appears that it is completely subjective! I am sure you can bring whatever is reasonable. You will have to buy juice/milk/water on the other side before getting on the plane though.
One other tip, I carry several $5 Starbucks gift cards with me. When someone goes out of their way for us, I give it to them. It isn't much, but when you are loaded down with car seat, stroller, luggage and worrying about food/water for your kid, anyone who goes above and beyond for us I like to thank in this way.
Good luck!