I wouldn't bother with buying a special stroller. Lots of airports have them or you can use your normal stroller until you board and then hand it over. I just use the little trolleys to wheel the little darlings around on stops. Other people swear by them but I think they're just extra luggage and not very efficient strollers. Also try and encourage your DS to run around the airport when you stop.
Take a change of clothes for everyone - if you get something gross or a cup of juice over you it's nice to be able to change.
Take some old favourites as well as new toys. My boys like something familiar when things get a bit stressy. Books are good. You will probably get some kind of activity pack on the plane. Pencils are good but only about 5 so you can put them in a cup and enforce a one at a time rule. They roll for miles when they fall. Stickers are fun but only for when you feel like watching like a hawk because it's no fun if they stick them on the wrong place.

Try to fly mid-week because flights are often emptier then and ask when you check-in to be seated near an empty row. If you spot an empty row chuck something on it to claim it or move into it before take-off. Having those extra seats can make the difference between a great night and a night from hell.
Try to find a flight that leaves in the evening - your toddler will probably sleep through most of the first leg if you can do that.