Mobile travelling equipment
Prams and backpacks ( and it feels like the kitchen sink too when you line up all the bags to take to the airport!)
Backpacks - We had a macpac pack to carry our child in. Great to wear but too big for take on luggage. I decided that if we were to do it again with a young child who needs carrying at times that a fold up pack like the Ergo is the way to go. That way you can use it in airports and it is so much easier than lugging a big pack around and you have free hands when your toddler is in a pack. They all seem to double as an infant front pack and then as the child gets bigger a back pack.
A Stroller or pram is good for cities when even terrain, allows your child to sleep and rest when needed too. We always had so much stuff that we opted only once to take a small stroller and it was great as carrying your child in a pack a lot on hard pavement tends to give you a sore back. I wouldn't bother having one for the airports again as most international airports tend to have them available for you to use in transit areas and if you had a soft style backpack you could use this instead.
We found a portable DVD great as the movies in the back of the seats on planes tend to be too high for a little one to see properly. Our rule about limiting TV time does not exist on planes - anything to keep a small child happy on a long flight was good for both us and passengers around us!
Stickers and a roll of masking tape - fantastic for 2-3 yr olds. Buy the painters (usually pale green or blue) from the hardware store as it is low residue and let your child show you what you can do with it. Easily cleaned up at the end of the flight and we got some very interesting creations from unused paper/cutlery etc from the meal tray! Colouring pencils and paper always seem to work well for us. Also when our daughter was smaller I always got one or two new plastic animals to add to our collection and wrapped them up to bring out as needed on the flight . LOTS of snack food is a must as well as often kids sleep through meals and much easier to have favourite food with you.
Lastly we bought a CARES flight safety harness http://www.kidsflysafe.com/ which we have found great. Because our child is so used to car seats she was fine with this and it stopped her from wriggling out of the lap belt etc as small kids are prone to do. Only issue on long flights was sleeping as she just couldn't get comfortable in it, so used to lie across the seat with the lapbelt across her hips midflight but I would buckle her in for takeoff and landing. Only once we were asked not to use on an air japan flight where the hostess said she had to be able to lean forward to brace against the seat in front ( like she could reach when her feet only just came off the edge of the seat) . Despite my explanations that the reason for using the harness was she could not brace this way they insisted we removed the shoulder straps. (I did this and as soon as we were going down the runway and the staff were seated where they could not see I buckled her back in) . Read all the data at kidsflysafe above as they explain it well.