I took DS (4 months) this past weekend (by myself) for the first time and he was AMAZING! Better than on land! The white noise sound of the plane lulled him to sleep, I think!
Bring a pacifier to help with the pressure change. Bring premade formula or BM (they will not let you bring on water bottles and the powder to mix later). Change him into his PJs if you are traveling during his bedtime so you can do a quick move right to bed once landed. Even if you do not have a ticket for DS and are planning on holding him, ask the counter person if the flight is booked or not. If it is not fully booked (and if they will let you), bring the carseat with you on the plane so that you don't have to hold DS the whole time, especially if he falls asleep. I have a "Snap and Go" and a Peg Perego carseat that sets in the stroller and I brought those with me (gate checked the stroller upon boarding and simply strapped the seatbelt around the carseat on the seat next to me).
Re: Taking LO on a plane for the first time tomorrow
I took DS (4 months) this past weekend (by myself) for the first time and he was AMAZING! Better than on land!
The white noise sound of the plane lulled him to sleep, I think! 
Bring a pacifier to help with the pressure change. Bring premade formula or BM (they will not let you bring on water bottles and the powder to mix later). Change him into his PJs if you are traveling during his bedtime so you can do a quick move right to bed once landed. Even if you do not have a ticket for DS and are planning on holding him, ask the counter person if the flight is booked or not. If it is not fully booked (and if they will let you), bring the carseat with you on the plane so that you don't have to hold DS the whole time, especially if he falls asleep. I have a "Snap and Go" and a Peg Perego carseat that sets in the stroller and I brought those with me (gate checked the stroller upon boarding and simply strapped the seatbelt around the carseat on the seat next to me).
Good luck!