I am also going to bring: some crayons and paper; B’s pretend set of keys (my mother-in-law made them for her out of real keys that she painted and made an adorable keychain;) antibacterial wipes to wipe down the seat, the tray, the window; toiletries (hand sanitizer, chapstick); and pacifiers.
Prior to having a kid we absolutely NEVER checked bags. But it is inevitable for easy travel with a kid. Theoretically we could do without the pack n’ play (if we co-slept or were staying where there was), held B on our laps for all meals, and wanted to hold her over the potty all week, and weren’t driving back or taking a car to/from the airport we could avoid the car seat. BUT…we don’t have any interest in doing the above and would much happier check the bags then deal with the sacrifices all week. From what I read in my research for our first trip last year and our experience, check everything you can so you aren’t lugging everything through the airport the whole time. We always have our necessities with us (medicine, extra pair of clothes, diapers) so we can survive for a day if we lose our baggage. Now cross your fingers we don’t lose our luggage and don’t hit any delays!