The first thing that springs to mind is get onto any feeding issues early - line up help before you have your baby. It is going to be sooooo much easier if you're breastfeeding. You're sitting down anyway, so can just feed constantly if your little one is unsettled.
I didn't fly with DS till he was much older, but can't really think of anything else essential - carrier, wipes, spew cloths and changes of clothes, yep