D.B.
I think a stroller is a huge help in the airport, and it can be "gate checked" by the flight attendant so you can roll it right up to the door of the plane. Since you are changing planes, that will be a huge help at the mid point. Put your purse in your suitcase for use when you get to your destination, and check your bag even if there's a fee. Put your wallet and cell phone in the diaper bag so you only have one bag to carry. The water bottle sounds like a cute entertainment item, but remember you cannot take water through security. Take an empty bottle and fill it afterwards. Definitely get new toys that he hasn't seen, and don't get anything too noisy because it can annoy the other passengers. Try to feed him (nursing or bottle) during take off and landing, for the ear pressure. That means don't feed him beforehand - make sure he's a little hungry. Wear slip on shoes so you can take them off at security and not be bothered with shoelaces or straps. Take a sweater or a sweatshirt with you so that you can use it as a pillow to support him if he sleeps in your arms. All that dead weight can be a real problem! If you can take the car seat on the plane, it is helpful. If there's an empty seat next to you, the flight attendants might not make you pay for it. If there are empty seats on the plane, often a nice person sitting next to you will be willing to move to give you extra room. That doesn't mean they think your baby is annoying, although some people will happily move just in case! The flight attendant can ask them if you don't want to. And remember that you can pre-board with infants so you aren't standing in the aisle waiting for everyone to get their stuff in the overhead compartments. Some people like the bulkhead seating because there is extra leg room, and others don't like it because there's no place to put your stuff during takeoff - there's no seat in front of you, you know?
I agree to pack light and let your family help out on the other end - tell them what baby food you need and see if they can borrow some toys or other items from neighbors or even a rental place.
Dress in layers yourself so you can peel things on and off as the temperature on planes can vary. Dress the baby in layers too.
Have a good trip!