According to Randy Quaid, many of cousin Eddie's characteristics (most notably the clicking of the tongue) were based off a guy that Quaid knew from when he grew up in Texas years ago who had similar traits.
After Clark Griswold (Chevy Chase) unsuccessfully attempts to demonstrate his handiwork with the house Christmas lights to his family, he asks his son, Rusty (Johnny Galecki), to help him check all the light bulbs again. Rusty looks at his bare wrist, pretending to have a watch, and excuses himself. Looking at a bare wrist and pretending to have a watch is one of Chevy Chase's trademark gags.
The movie is based on John Hughes' short story "Christmas '59", the second Vacation story to be published in National Lampoon's Magazine (the first was "Vacation '58", which was the basis for the first Vacation movie). The Christmas story was printed in December 1980. The label on the home movie reel that Clark finds in the attic is labeled "Xmas '59," a further allusion.
When Clark and Cousin Eddie are talking in the living room, they are drinking egg nog out of Wally World mugs. Wally World was the destination of the Griswold's in the original National Lampoon's National Lampoon's Vacation (1983).
According to an article on the making of Home Alone (1990) in Chicago Magazine, Chris Columbus states that he was the original director of this movie. Although he filmed some second-unit establishing shots (which he claims are still in the finished film), he left after two meetings with Chevy Chase and told writer/producer John Hughes, "There's no way I can do this movie. I know I need to work, but I can't do it with this guy." He was sent the script to Home Alone in its place.
When Eddie barges in the house with Clark's boss, Ellen jokingly tells him this is the family's first kidnapping, which is actually wrong. In National Lampoon's National Lampoon's Vacation (1983), Clark kidnaps the security guard at Walley World and forces him to take the family on the rides.
When shopping with Clark Eddie asks Clark if it was his company that "killed all those people in India". He is referencing the Bhopal disaster, also known as the Union Carbide disaster in which leaks from a Union Carbide pesticide plant escaped into the air. Thousands of people died and many more were sickened.
The Warner Bros. back lot used for the neighborhood in which the Griswolds live is the same as the one used on the TV series, The Middle (2009), which featured Brian Doyle-Murray (Mr. Shirley) in a recurring role as Mr. Ehlert for the first three seasons.
Just before Clark gets locked up in the attic, he pulls out an old present from a hidden slot, and it contains a card that reads "Happy Mother's Day 1983, Love Clark". The first movie, National Lampoon's Vacation (1983) was released that same year.
In the scene when the police storm into the Griswolds' house, the song "Here Comes Santa Claus" sung by Gene Autry is used for the background music. Randy Quaid (cousin Eddie) is the third cousin of Gene Autry.
Cousin Eddie explains to Clark that his older kids couldn't make it because his daughter was "at the Clinic getting cured off the Wild Turkey" and his son was preparing for his career as a carnival worker. This is a reference to Cousin Vicky and Cousin Dale from National Lampoon's Vacation (1983). Cousin Vicky would return once again in the following film, Vegas Vacation (1997), as well as Ruby Sue from this film (though played by a different actress).
Brian Doyle-Murray appears in two of the Vacation movies. In Christmas Vacation he plays Frank Shirley, clark's boss. In the original Vacation movie Murray plays the Kamp Komfort clerk where the Griswold's stop to stay on their way to Wally World.
A Wal-Mart storefront appears in the film with an empty parking lot - during the film's release Wal-Mart did not have their stores operating 24 hours when the chain was remodeled a few years later when the company converted their stores to hypermarkets (similar to its Sam's Wholesale Club stores without the annual membership fees). In real life, the slang for Wal-Mart is known as Wally World (appropriating the name of the Walley World theme park from the first film when referring to a box retailer).
All the presents that are on the credenza when Clark goes in to give his to Mr. Shirley are identically shaped and likely the same gift. It is a desk organizer. When this movie came out, pen sets came in an L-shaped arrangement. The writing instruments were on the flat part and the raised section held post-it notes. Paper clips and other holders were also a possibility.
Cousin Eddie has a son named Rocky wearing a Las Vegas shirt. Coincidentally, footage from this film appears in the film Rocky V (1990). Furthermore, the next film in the series would be Vegas Vacation (1997).
In several outdoor scenes at the Griswold home a 1963 powder blue Lincoln Continental convertible can be seen parked out front. This was the last of the curved glass slab sides and is sought after by collectors. The 1964 Continental convertible had straight glass windows to provide more interior space.
John Hughes was asked if he wanted to write a new film for the Vacation series. He said he would only do it if he had a good story to use, as by this point the franchise was a Chevy Chase vehicle and there was little need for him to write a story. He found one called Christmas '59 from his time working at National Lampoon Magazine that he thought was good, so he agreed to write the script.
The messenger that delivers Clark's Christmas "bonus" is wearing a jacket that reads "Speed Ball Messenger Service". "Speedball" is a street term for a drug cocktail of heroin and cocaine. The same mixture that killed John Belushi 7 years earlier.
When Clark shows his coworker Bill the brochure about the swimming pool he wants to put in his backyard, he is seen drinking coffee out of a Tasmanian Devil coffee mug. Miriam Flynn (Cousin Catherine) would later go on to play the voice of Taz's mother in the cartoon Taz-Mania (1991).
After failing to get the Christmas lights to work one last time, Clark Griswold (Chevy Chase) takes his frustration out on the plastic decorations in the front yard. Chase actually breaks his pinky finger while punching Santa Claus. He resorts to kicking and clubbing the decorations after that. The film kept rolling and the take was used.
When Clark has the tirade and says "We're gonna have the hap hap happiest Christmas since Bing Crosby tap danced with Danny Kaye" This was a nod to the movie "White Christmas" (1954) which starred Bing Crosby and Danny Kaye.
The trivia items below may give away important plot points.
The scene where the cat bites on the Christmas lights cord and gets electrocuted was nearly cut from the movie. Prior to the first test screening. the studio execs wanted the scene taken out, fearing that it might offend some viewers, but producer Matty Simmons begged them to leave the scene in, and they eventually gave in to his request. After the first test screening, the test audience had scored the cat electrocution scene as the No. 1 favorite scene throughout the entire movie.