I just took my 2 year old daughter and 13 month old son to Hawaii. We flew direct from Denver on the way down, and stopped in LA with a layover on the way back. We SURVIVED!!
My question at the time was about the time change - 4 hours behind is a lot. Both kids acclimated pretty fast to the evening change (they went to bed between 7:30 and 8:00), but my 2 year old was up really early the first two days. I put her in the bathtub while brother and dad slept and when brother woke up, we went outside to see the sunrise. Just try to do things at the normal time - if you eat breakfast here at 8:00, then eat there at 8:00. It was harder for them to adjust back to Colorado time when we got back than it was to adjust to Hawaii time.
Now getting there...It was a long plane ride, and I have to say I LOVED the looks everyone gave us as we got on the plane (jerks...). Anyway, we packed Color Wonder coloring books and markers so my daughter did not color on the seats, window... She read books, did a puzzle and colored a picture for the pilot. We took a DVD player and she watched a movie when she began getting tired and took a great nap. We had 4 seats but my son sat on my lap most of the time, so she was able to choose between 2 seats and that kept her active.
About 3/4 of the way there, they were both antsy so we did laps around the plane (I assume yours will be a large plane with seats in the middle). I did not allow them to run and they had to walk quietly in the middle of the aisle.
Snacks are tough. Can he have peanut butter? Celery with peanut butter, raisins, pretzels, saltine crackers, animal crackers (do those have dairy?) would all be easy to tote.
We have been to 3 different islands in Hawaii and at each airport there is a long haul from the gate to the rental car or pickup area. Just one more thing to think about...
Have fun and don't fret - all will go well!