My biggest tip would be to if your flying pack ALL your little ones night time stuff in a carry on, down to soap/lotion, night lights, everything you could possibly need for bed time that way if the air line loses your luggage you at least will have his stuff for bed time and that will at least make your life a little easier.
As for extra stuff, my family apparently goes through socks like crazy, we went for a week and brought 10 pairs of socks and used all 10 pairs (for DS) and could have used more. I would bring saline/nose sucker, vicks, Tylenol and Motrin (in case of fever), thermometer ect. It may seem like overkill but I can't think of anything worse then a miserable baby at 3 in the morning. Hopefully it wont get used but if it does you'll be glad to have them. Oh, and count on at least 10 more diapers then you think you need.