Keep his diet and routine the same as much as possible.
Most airlines will allow you to take the pushchair right up to the plane door and then staff will pop it under with the luggage. Ask at check-in whether you get it back on the Tarmac once you've landed or whether it will turn up on the carousel.
You should get priority boarding.
You should try and give baby a drink whilst taking off and landing to relieve any pressure in his/her ears. Either that or encourage them to suck their thumb (that works for longer!). Take satchets of Calpol and ibuprofen with your hand luggage just in case. Make sure you have at least one change of clothes for him on the flight and bring a spare top for yourself. Just in case! Layer him up so you can keep him comfy through the flight.
You can pre order your baby food and formula to the boots at the airport so you don't have to worry about getting liquids through etc. I travelled with one bottle and then took 2 pre sterilised bottles with me and bought cartons at the airport for both outward and inward journeys. Starbucks in Terminal 1 will heat baby milk behind the counter, as will Brodericks in Terminal 2 and Costa and Caffe Nero in Terminal 3.
Several dummies for the plane if your baby uses them - then if they get flung on the mucky floor you can get another one out.
Are you taking a car seat? If you're hiring a car, I would seriously consider taking your own car seat. The car seats that come with hire cars in my experience have been awful and dangerous.
If you're using bottles, take a travel steriliser or buy a washing up bowl out there and use Milton sterilising tablets.
I always bought my nappies on holiday- just the local brand but I brought swim nappies - they were much more expensive. Also I found that not many places sell nappy bags.
Take a universal bath plug any plughole. It's useful for turning any basin into a baby bath. A pair of socks over the taps will prevent him from turning them on. Also pack a plug in night light which will be useful for getting up for nappy changes etc..