Scott has made some really good points.
You may find these Travel toys for infants to be useful, particularly the "blue tape".
If at all possible try and schedule a milk feed to be given during or just after take off, we always found that our daughter was able to fall asleep easily and then wake up more cheerful and playful. (This was on flights of about 4 hours) I think the whole process of getting to the airport, checking in and finally sitting down in the plane is really tiring for the little ones too )
This way you avoid extensive grogginess and your little one wakes up rested and eager to play and check out his surrounding.
Finger foods that he can feed himself with, and some juice drinks are great and as Scott says the pamphlets, magazines in the back seat pocket are very entertaining. If you carry a marker pen handy you could create a monster puppet out of the "paper bag" provided for airsickness.
Try and take a picture of him, while he is sleeping, this picture will come in handy later on as he gets older and you talk or explain to him, about how he slept during the flight, whilst preparing him for other plane journeys. Our daughter would respond with questions about it... and it was a great way of making her understand the different bits of the journey.
Additionally the website Delicious Baby could be quite useful too, with many articles related to travelling with babies, toddlers, and young children.
Have fun!
