Big-selling authors may get access to the set when their movie is adapted to film, or may get introduced to the band doing the soundtrack, but most authors never meet anybody famous except other authors.
Usually the author of the source material (novel) is *not* welcome at the set where they're making a movie of it. (Neither is the screenwriter.) The director and actors do not contact the author for insight into the characters, and the band doesn't have any reason to meet the author at all.
So if you want to rub elbows with celebrities, becoming an author probably isn't the best approach.