My advice is to ask for anything you need well before you *need* it.
If you are still breastfeeding, don't wean before the travel...it's much easier to travel with a breastfed baby - food on tap and it helps with the ears too...
I packed bundles with one light change of clothing, nappy, couple of wipes in ziplock bag, cloth nappy and a spare plastic bag - dad could grab bundle + baby and take off straight for the bathroom in case of imminent nappy disaster...
My only strong advice would be don't be tempted to use sedatives...when we came over from Sydney to zurich there were at least three kids who travelled really really badly - at least when your child is not on drugs, you can tell by looking into their eyes if they are feeling not so good - one girl about 6-7 puked her way all the way from Singapore, and guaranteed it was from 'medicine'...also I suspect long-term it probably doesn't help with fear-of-flying since the child will associate airplane travel with being out of their brain...sorry that's harsh, but it wasn't a pretty sight...
Oh, and ask for plenty of extra drinks for yourself as well - no need to suffer the flight...
If your child is walking/moving by that age, it's 21+ hours travelling - take them around the plane at every suitable opportunity - don't try to confine them until you have to.
Seatbelts are also a big problem for some kids - actually, you can make your best effort to put them in, but I have asked a couple of times if seatbelts are *compulsory* and airline staff have not said yes...if the choice is between having a screaming baby in a seatbelt, or a calm baby who is not in a seatbelt I'd go the latter - a little waistband really isn't going to do much in an emergency...
For toys/activities, choose some small items and wrap them like presents - things that are their favourites...and open one at a time...make it last as long as possible...
For us, one-way wasn't so bad - but I'm not looking forward to next summer when we plan to do the round-trip with three children aged 2,8 and 10...