How would you do it?

I have not seen this movie. I rented the movie once, but the DVD was scratched and I didn't really care to struggle to try to see a film which was widely regarded as a dubious adaptation of an already difficult to adapt book.

That said, in my head I have visions of what a Breakfast of Champions movie done right would be like. For one, it would be filmed somewhat like a deranged documentary. The narrator would pop into frame to explain people about various things such as "wide open beavers" or whatnot, holding up pieces of cardboard with Vonnegut's pictures on them. The narrator would also repeatedly talk about Vonnegut, about how his own life inspired various bits of the film. While walking into the scene, he would flagrantly interact with the scene, and he would more or less take the place of Vonnegut's own self-insertion bits. He would give the "Breakfast of Champions is a registered trademark..." spiel every time the phrase is uttered.

In addition, I decided while reading Slaughterhouse Five that in a few decades when he has been suitably aged, Johnny Depp might play a very interesting Kilgore Trout. There was something about how he acted in his scenes in Slaughterhouse Five which really felt like how Depp played Willy Wonka, and if you make his Wonka a much more pessimistic and world-weary person, (which is a big change, granted) you might not be too far from Trout.