If you can, take little toys and activities that are new to the child.....this will keep their attention longer than toys they are used to. Stickers are good too, and those little travel magna doodles. I also take special snacks....for example, I usually do not give my kids rainbow goldfish because the colors freak me out....but I do take them on the airpane! It also helps to take the child's comfort items....a blanket and/or stuffed animal. And a portable dvd player always comes in handy....and we usually buy or borrow a new dvd that they have not seen yet. And it is so much easier if they have their own seat with their carseat. I know it is a pain to carry the carseat through the airport, but it is sooooo worth the trouble!
As for the benedryl......if you want to try that apporach, then test it out first before you go! It has the opposite effect on alot of children.....I know people who have given their kids benedryl for the first time before a flight and it was a nightmare because it made the kids hyper and cranky.
And the most improtant advice.....try to stay relaxed no matter what....ignore rude stares or comments from other fliers if your kid is acting up or kicking the seat in front of him/her .I always warn the person in front of my toddler that she will probably kick the seat, and while I will do everything in my power to keep her from doing it, it WILL happen because she is a toddler! We fly southwest, so this lets the person choose another seat if they want! But I have always had very understanding parents in front of me, so we have never had a problem with anyone getting mad (of course this only applies to toddlers.....if the child is older, then they should not be kicking the seat in front of them). I hope your toddler does great, but if they don't....just remember that the flight will eventually be over. You'll get through it!:wave: