Bring toys that don't have too many pieces or make a big mess. Quiet toys will be appreciated by the other passengers. Bring an extra blanket for your baby. The airlines have blankets but it s not a guarantee that you can get one. Always bring a sippy cup, which is great for drinking on take off and landing to help ears pop.
Suckers are also good for take off and landings.
Most airplanes have at least one changing table, albeit a small one. The changing tables are usually in the restrooms. The major complaint about flying babies are when a parent changes a stinky, yucky diaper on the seat. The air on the plane is already bad and there's nowhere for the smell to go. When an airplane does not have a changing table you will have to make do.