Hey C.,
As a routine flyer who did it more than I intended with a little one...here is what I know.
To keep kinds occupied.... snacks (PB crackers, Goldfish, Cheerios, fruit, etc.) No fruit if leaving Country though.
Toys (Books, Ipod, Nintendo DS, etc.) Since we travelled with an infant I brought baby toys and again as a toddler I brough hard, musical and light up toys that had a low volume, then later as a toddler I brought the laptop and some movies and of course our favorite stuffed animal. Think of this like a long car trip and pack as if you would for that.
What to expect... most kids do quite well flying and so all you need to really expect is the rush of getting situated and of course them being tired after crossing through the airport.
EARS MAY POP....If you have an infant, you can get some sugary syrup to dip a pacifier in or feed your baby as the plane takes off and lands to keep thier ears from popping. If you have a small child, then suckers and drinking juice are great to have on hand.... and if your child is old enough and for yourself.... bring gum and chew it at take off and landing.
As for what you can not have..... no liquids in containers larger than I think 4oz... check you airlines website... and all of you tiny containers like hand sanitzer, liquid makeup, lotion, etc must fit into a quart size ziplock per person and must be removed from carry ons and placed in a seperate tray at the safety scanning. Now I do know that when I travelled with my little one, the ready made nursettes were 6oz.... and since they were closed and it was for a baby I was allowed to travel with all the closed ones... so we discarded the open one and opened another once on board. You may want to call ahead and see if you can pack tiny juices for your little ones in thier quart size ziplock bag. I know when we travelled as a toddler and because of severe acid reflux, my daughter could only have "white grape juice", so not something you could purcahse past security... I just brought a doctor's note and anytime I had a problem.. I just asked for the supervisor... they were all nice and just doing their jobs...once they heard the issue and saw the note, they nodded me through..of course I had to dispose of the open one again.
Things you can not have on board a plane beside liquids,... NO knives, pocket knives, screwdrivers, mace pepper spray, razor blades, lighters... etc... all this will be listed on the airlines website also call and check the airports security guidelines.
As for carseats.... if you purchased your child a plane seat... required depending on age... you can bring and use the carseat on the plane. your choice. and if you wish to bring it for the trip but not the plane... MOST airlines let carseats go in cargo free... you will need to ask. And if they let them go free this does not count as part of the number of luggage you allowed to carry. You will check your carseat if not using on the plane at the same place you check in all of your luggage. Just remember you will be carrying all of this, luggage and kids. But carseats are a necessity. And thank goodness you get to lessen the load hopefully curbside or just inside the airport. The rest of the journey is through the airport, security and then boarding.
THE BEST THING EVER>>> Bring your stroller. These are allowed free and can be taken right up to the plane gate and then "check them at the gate".... they can be driven down the loading corridor and folded and left right outside the plane with a gate check tag... and they will be at your landing in the same spot as the flight crew, etc stows them away and brings them back for you. I cna't tell you how many times we brought the stroller and how handy it was .... This is a must have depending on the age of your little ones.
Best Wishes... Flying is fun and to see your kids look out the windows at the world is so refreshing. May you have a safe, fun and wonderful trip.
-MB