Charles Chaplin, or better yet to just hang around the set to watch him work.
Hitler -- to sit down with him and ask him "why?" and that somehow he is compelled to speak the truth and answer honestly.
Dinosaurs -- to be put in a safe cave or hillside where I can watch them without getting hurt, watch them walk around and feed, etc...with the proviso that somehow I will be returned back in time to the present day. I wouldn't want to be left all alone with a bunch of dinosaurs!
:lumpy