Flying with Baby

Hello ladies! I've never posted anything but I had a couple of questions regarding traveling with my 10 month old son so any input is appreciated. I haven't flown in years and I will be taking a somewhat short flight from Phoenix to California. I was wondering if I'm allowed to take formula on the plane in a travel dispenser container (like the one below)

or does it have to be like in a new sealed package? Also I'm flying with American Airlines and I wanted to purchase one of those gate check bags for his car seat online but some people online were saying that American sells similar ones at the gate... have any of you ever purchased one at the airport? I just don't want his car seat to get damaged. Thanks in advance 😊