Here are some thoughts:
[list][*]Ride the Batmobile[*]Pull your lightsaber and oppose Darth Vader[*]Wear the coolest shades ever and stop bullets in mid-air[*]Fire photon torpedoes and see those nasty Klingons go bye-bye[*]Websling high above the streets of New York[*]Save the world using wit and wodka-martini's[*]Have the gut to say it to Ariel's face
[list]
I know, I know... ideas are a bit boyish here and there, but give me a break. I'm a guy. Girls are free to fill in.
Be creative and make others experience the joy of the "now why didn't I think of that" moment.

[EDIT] (to avoid further misunderstandings)
This topic is ofcourse about being/meeting fictional characters while dreaming, and not in real life. Some people do wish for the latter, to which I only have this to say: Not gonna happen! (or more appropriate: In your dreams, buddy!)