I traveled with my 2 1/2 year old and 4 year old over Christmas by myself this year and decided for little ones, a car seat is the way to go. They can't get out. It is MUCH safer for them in case of some air emergency, and it is more comfortable for them to sleep in (which every mom hopes they will do on the plane). To make it easier, I bought these great wheels to attach to my carseat so I could strap my kids in, pull up the handles, and walk through the airport pulling them just like you would pull a suitcase. They loved their "rocket seats" and so did I. Try gogobabyz.com for the wheels. Worth every penny I paid to get it here on time.
On my international flights I could actually roll the car seat down the aisle (but on domestic flights the aisle was too narrow). On one flight, my little one was asleep when we landed so I asked a strong man sitting near me to just carry him out in his car seat, it was great and he didn't wake up. I just rolled him through to baggage claim.
I also took empty water bottles with a sports top/straw top with me so we could refill with water along the way. That was much easier than trying to get either of my kids to use a regular cup while bumping up and down on the plane.
Take snacks you know they will love in case the food is not edible.
And get creative on activities. We went through a lot of pipe cleaners making animals and bracelets and buildings... they are light weight and can be reused, so they are a great option. playdough was too messy, i thought. legos are good, but expect to be on the floor often trying to retrieve them. little plastic animals were a big hit. i doled them out along the way.
If I had been more organized, I would have wrapped each of their travel toys individually to make it even more fun to open. For me, the biggest thing was how can I fill the next five minutes. A present wrapped wtih lots of tape takes more time than just a toy, so I am all about the delay.
Hope some of this helps. Good luck!