At the very end of the film, when the group uses the Improbability Drive to go to the Restaurant at the End of the Universe, there are a lot of images that flash onto the screen when the drive is activated, so in the other parts of the film. In this case, the very last image shown is the face of Douglas Adams, the creator of the Hitchhiker series.
As they enter the temple of the Jatravartid people of Viltvoldle Six, at the base of the stairs is a "perfect recreation of Douglas Adam's nose" (DVD commentary) modeled from a cyber-scan of this head that had been previously created for a game and used in the film as an homage to him following his death prior to the completion of the film.
The rather old-fashioned car that Ford tries to introduce himself to and nearly gets run down by is a real Ford Prefect.
The various nose sculptures in the temple of the Great Green Arkelseizure are based on Douglas Adams' own nose.
The hymn we hear in the temple scene was recorded in Douglas Adams' local church and dubbed over the scene.