I see you have a ton of advice already, but I figured I'd throw mine into the ring. I haven't read through all of the responses, so sorry if I'm repeating things. I've flown twice (4 flights) with my daughter, once at 3 months with my husband, and once at 4 months by myself. I'm planning another one in September (8 months) that will be solo, and longer.
My biggest advice is wear your baby in the airport. It makes life soooo much easier. I used the Bjorn, then ring sling, and will use an ERGO on the next trip. You can wear your son through security, which is very, very nice. However, on the plane you cannot wear your baby during take off and landing, which I through was ridiculous but is apparently FAA regulation. So be prepared to pull him out during those times.
I packed breast milk on the first flight, but my daughter is a big nurser so it wasn't an issue for us - I haven't bothered since. You can bring any amount of breast milk through security - just tell the person checking your boarding pass that you have it and they will typically tell you who to talk to {if anyone, my experience varied) to ensure it goes through without a hitch. Nurse on take off and landing, or have a pacifier (if he'll take one), if possible because that'll help with the ears.
Airlines all differ on how much you can check and how gate check works, so check with yours. I flew Southwest on one of the flights - my carseat and stoller together counted as one piece of luggage, but I chose to gatecheck the stroller to avoid it going through the main luggage system. It didn't work - on the way back they sent it down to main baggage for the flight and it went through the carosels and everything. Be vocal about gate check meaning just that if you choose to use it!
Extra clothes are a must, and an extra shirt for yourself isn't a bad idea. My daughter had major blowouts, probably helped by the pressure changes, and it was really nice to have extra clothes. At 2 months your son will likely sleep (I sit in the very back of the plane so engine noise will help keep my daughter asleep), but if he likes any small toys pack
'em for distraction. Ask the flight attendants when you board if there is a restroom with a changing station in it so you know which one to go to - if there isn't one they will probably let you change him on the floor back in their area (that was offered to me on multiple flights on older model planes without changing stations).
Finally, check the TSA website for the current story on carrying on creams and liquids. I combined all the diaper bag liquids/creams with my own in the single quart-sized baggie, but it meant packing a special tube of diaper cream since my usual one was more than 3 oz. This probably applies to sunscreen etc. I THINK there may be some exceptions, but I'd check the website to be sure.
Good luck - it'll probably be WAY easier than you're expecting!