The booth that Amy inquires about hemp actually has "of" twice in its sign. It reads: "Dudes For the Legalization of of Hemp." Many people's brain skip over the the second use of the word. (Just like that last sentence). And it doesn't say "legalization" either - it says "legalation".
The "Scary Door" sequence is a parody of "The Twilight Zone" (1963) season one episode, "Time Enough at Last," where, following a bomb blast, the last man on Earth (Burgess Meredith) indeed finds himself with a library full of books and nothing but time to read them all, before his large coke bottle glasses break, leaving him to lament: "It's not fair! There was time now!"
Nixon saying he would just as soon give up his new body as give up his dog Checkers is a reference to his famous "Checkers Speech," where he admitted that he received Checkers as political gift but would not be giving him up.
The hopelessly stoned hemp dude says "Dave's not here, man." In the early 1970s the comedy duo of Cheech and Chong started the genre of stoner humor and their "Dave's not here" skit was their brilliant signature piece.
Included at the Head Museum are movie stars Charles Chaplin, Jack Nicholson, Clint Eastwood, Leonardo DiCaprio, Tom Cruise, Nicole Kidman, Sylvester Stallone, Sharon Stone, John Turturro, Eric Stoltz, Mimi Rogers, Martin Lawrence, Elvis Presley, and Sarah Michelle Gellar; porn stars Ron Jeremy, Traci Lords, Long D. Silver, Jill Big Breasts, and Samuel Genitals; and television stars Lucille Ball, Jerry Seinfeld, David Duchovny, Gillian Anderson, Tim Allen, and Katey Sagal (the voice of Leela).