Quite simply name a character you want to see in the game, the character can be from something such as a comic book or another game or a character you created your self.

parties with dragons.

Richtofen.

Gunny. I want a cigar chompin, butt kickin squad mate

All other curiors.

http://fallout.wikia.com/wiki/Chance.

Why'd he have to die...
He should have been near death and then we can come along and fix him up, making him a new companion. (He's really powerful but he needs medical attention quite often.)

Duke Nukem

Captain price

Vincent Price (any of his characters).