Change of clothes
Bib
Wipes
(My kid had a blowout diaper, spit up, or major food spill on every flight we took up to the age of two years!)
Consider a CARES harness and check your car seat, if you think she'll accidentally (or intentionally) kick the seat in front of her.
Keep away and peek a boo are good games for while you're in the seat. Walking the aisles is good as long as you're not blocking other passengers and the fasten seatbelt sign isn't
http://m.georgetownuniversityhospital.org/body_dept.cfm?id=556685