Bill and Ted playing a game with Death to win back their lives is a reference to the classic Ingmar Bergman film, The Seventh Seal (aka The Seventh Seal), in which a knight plays chess with Death for his life.
The mountain to which Bill and Ted are brought to be killed by the evil robots is the same mountain Captain Kirk climbs in "Arena", the episode of Star Trek that Bill and Ted watched in their apartment.
The evil robots arrive in the parking lot of the Circle-K convenience store, the same place where Bill and Ted first meet Rufus in Bill & Ted's Excellent Adventure.
When Missy and her friends are trying to send Bill and Ted's ghosts to hell, the words they chant spell, "Ed and Chris will rule the world," backwards.
In the scene where Bill and Ted are addressing God, there are 2 statues at the base of the staircase. One is of Michael Powell and the other is of David Niven, an homage to Powell and Emeric Pressburger's afterlife classic Stairway to Heaven. The stairway itself is the same as the one in that film, which has the USA title "Stairway to Heaven".
When Ted attempts to get into Heaven by proving himself worthy, he says, "Every rose has its thorn. Every night has a dawn. Every cowboy sings a sad sad song." These are the key lyrics of "Every Rose Has Its Thorn", a song sung by the popular 1980s/1990s heavy metal band Poison.
The guitars that Bill and Ted play are a Gibson SG Standard and a Gibson '59 Flying V. Ted plays two different color schemes on the V, while Bill's SG was the same throughout the movie
The guitar solo before Kiss' "God Gave Rock And Roll To You", is performed by guitar legend Steve Vai The footage had already been shot and the world premiere was a week away, when he was asked to do it. He also contributed various music in the film, including "The Reaper Rap", which features on the end credits.
When Bill and Ted go to Missy's séance, you can see Chris Matheson and Ed Solomon, the creators and writers of Bill and Ted. They're the only men that are attending the séance. (Chris is the guy with the white shirt and Ed is the guy with the glasses.)
The "Riddance of Evil" book that Missy uses to send Bill & Ted to hell is actually a redressed copy of the Stephen King short-story collection "Four Past Midnight." She opens it to a page in the story "Secret Window, Secret Garden," which can be read clearly in a few frames of the film.
Peter Hewitt:
The smoker in the Builder's Emporium to whom Death says, "I'll see you soon." In the cast credits The Smoker is credited as "Max Magenta".