The movie begins in 1947 in Moorcroft, Wyoming, where Paul crashes to Earth. In Close Encounters of the Third Kind (1977), Roy Neary (played by Richard Dreyfuss) travels to Moorcroft looking for an answer about his meeting with an UFO. The mountain where Paul signals his ship, called Devil's Tower, is also used in Close Encounters.
When Paul says, "Baby? Where we're going we don't need teeth" is an homage to Back to the Future; Doc Brown say, "Roads? Where we're going we don't need roads."
In the town where the comic book store shoot-out occurs, the movie theater marquee is announcing a double feature including Easy Rider (1969). The scene was filmed in Las Vegas, New Mexico, a block down the street from where Easy Rider was actually filmed. The other movie on the marque is Steven Spielberg's Duel (1971).
The normal eye of Kristen Wiig (Ruth Buggs) can be seen behind Ruth's blacked out glasses when Graeme and Ruth are arguing. Ruth's eye is meant to be deformed.
When discussing her beliefs with the guys, Ruth says that the world is 4,000 years old and can only be the product of intelligent design. Most Creationists believe that the world was created in 4004 BC, meaning that it is a little over 6,000 years old, not 4,000.
When Paul is going through the fridge for the first time in the RV, you hear Paul say, "Cool, Marmite." But the jar he pulls out of the fridge is actually a jar of Vegemite, the Australian version of Marmite.
Is this a part of the "Blood and Ice Cream" Trilogy?
A
No. The third and final picture in that trilogy was "The World's End". The first two films in the Blood and Cornettos Trilogy were co-written and directed by Edgar Wright, who is not involved in this movie.
Q
What are the differences between the Theatrical Version and the Extended Version?
A
For the home release, an approximately 5 minute longer version has been created, which is rather not worth much excitement. The various differences are all rather unspectacular and can be regarded as filling material. The shorter scenes in the theatrical version make sense mostly. Only a few acceptable extra jokes were added by the changes (Clive's shopping instructions or the nicked quote by Paul, coming together through extended scenes at the beginning and at the end of the film). Additionally, some characters are described a little deeper (Ruth's eye had not been medically treated because of the strong religiousness of her father). With many of these changes, some short moments of the theatrical release get lost - the term "alternative material" should not be taken too seriously, as it is often just an unspectacular different shot leading into the next scene. A detailed comparison between both versions with pictures can be found here.