Whereas Bill & Ted's Excellent Adventure relies on a misplaced in time storyline, Bill & Ted's Bogus Journey relies on a misplaced in death storyline. The Grim Reaper is clearly a parody of Ingmar Bergman's The Seventh Seal, though he's a lot less boring and quite spiteful in losing to Bill and Ted.
One interesting thing about this movie is that it goes a long way to show how Bill and Ted are largely the same person. When they propose to the girls, they give basically the same speech and ask, "Will you marry us." We also see them using the same lines at the same time. The first film was designed to keep them from separating, though perhaps if they did, they would become separate people... which would ruin the future.
One final piece of trivia that I noticed with my nerd-dar, the future school that Rufus teaches at is the Japanese Gardens at the Tillman Water Reclamation Plant in Van Nuys, CA. This site has also been used many times in the Star Trek series, most notably as Starfleet Academy. Later in the film, Bill and Ted are watching an episode of Star Trek where Kirk fights a Gorn at Vasquez Rocks, they are later taken there by their robot doppelgangers. This reference is more direct though, since they're purposefully drawing our attention to the same location.3
De Nomolos: Time will tell.
Rufus: Time has told.
De Nomolos: Then I will go back and change it.
1. Scrubs calls this "Guy Love", but I prefer the term bromance.
2. Of course, it's only a matter of time before Bros start having sex with each other that will somehow be not-gay. See Dude, You're a Fag by C.J. Pascoe for further reading on the usage of the term "fag" by high school males.
3. And to complete this nerd-out, Vasquez Rocks is also where the space ship was kept on the TV series Roswell. Coincidentally William Sadler who plays Death in Bill & Ted's Bogus Journey played the Sheriff on Roswell!