16-35 f2.8L II
last vacation 90% i shot with this lens
i did take a 70-200 which i didnt use very much but carried everywhere
the other lens I took which i used alot was the 50mm f1.4
+1. When I went to Disney, I mostly used the 17-55 f/2.8. I lugged a friend's 70-200 II, which was primarily used for stage shows and parades. If I were to go back, I'd consider leaving the 70-200 II home. I would suggest getting a fast 35 prime. It's nice for night time activities. Large aperture matters more than IS in this context because most of those pictures will have people in them and someone is almost always moving.
EDIT: Actually the 70-200 came in handy for animal kingdom too. If you have a secure place to lock up gear (and insured), then it's feasible to only bring a lens or two at any outing in the parks.