My main tip for flying with children is: Talk to them. Sounds obvious, but you'd be surprised...
Basically, an airport and a plane is going to be a strange environment for your child. He will need reassurance from you.
Before you go to the airport, play "planes" a few times (if you have time). Line up some chairs with ribbons round them (the cord from dressing gowns are good) as seat belts. Tell your child that you're now on the plane and need to fasten your seat belt because the sign is on (point to ceiling). Then do a "ping" noise after a little while and say the seat belt is switched off so he can take the belt off. Pretend to look out the window and describe what you see. And so on.
This will help you, as he will know what to expect when on the plane. Explain to him that it is just like being in the car and he needs to have his seat belt on just like in the car.
Praise him when he's good. Bear in mind that kids sometimes act up when they feel insecure and need your attention, but they don't know how to ask for it.
Bring favourite (small and soundless) toys, such as favourite teddy, book, and colouring book with crayons. Ask him to draw a picture for the pilot and the crew. If he just does a squiggle (as most often happens), encourage him to use another colour (drags out time).
Bring some snacks (preferably non-liquid items) to reward for good behaviour. Also bring an empty sippy-cup or similar for when the ears hurt (the crew can fill it with water/juice for you). Another one to try if the ears hurt is to play a game of doing the biggest yawn, as that sometimes helps.
And relax. If you're stressed, the child will be stressed. Write lists of what needs to be done before you go, so you won't forget anything, and it will ease your worries.
If you can avoid bringing a car seat, that makes it easier (or check it in), as airlines have different policies on which can be used and most car seats don't fit in the overhead locker.
Bring spare clothing (there will be accidents) and nappies. Also bring a change of shirt/top for yourself as you may be covered in something at some point.
If he cries and has a bit of a wobbly, don't worry too much. We know you're there and we know kids cry. It doesn't make you a bad parent.
The most important thing is to make sure he keeps his seat belt on when required. Hold him down in his seat if you need to. You're in charge of him and it's what you will be asked to do. He won't remember it, and you're looking after his safety at the end of the day.
Have a great flight, I'm sure it'll be lots of fun and he will probably enjoy it very much. Have a lovely time on your hols and try not to worry.
Hope this helps, sorry for long post.
Gg