Actor Allusion: As Tim Curry playing the hotel concierge flees from the hotel room in the second movie when he is threatened by a recording of Kevin's uncle, the recording says "Sing it, Frankie"...an allusion to Curry's previous role as Dr. Frank N. Furter from The Rocky Horror Picture Show.
Defictionalization: The Talkboy from Lost in New York was originally conceived as a non-working prop for the film; one letter-writing campaign from 1990s kids later, and it was Defictionalized by Tiger Electronics. It sold well enough that several variants were created, such as a pink-and-purple version called the Talkgirl.
Doing It for the Art: Daniel Stern was so committed to the role of Marv, and to the concept of Marv and Harry being the Wet Bandits, that in fact, a number of Marv's antics (sticking snowglobes to the dashboard with gum, stepping on and walking across glass ornaments, trying to pry open the back door with a crowbar before giving up and just opening it, the stupid look on his face before getting hit with a flying paint can, the "Why the hell are you dressed like a chicken?" line he says when he sees Harry covered in feathers) were ad-libbed by Stern.
Kevin's younger cousin Fuller is Macaulay Culkin's little brother Kieran.
The elf that Kevin meets before talking to Fake Santa in the first movie, and the New York airport desk clerk in the second movie was the then-wife of cinematography Julio Macat.
A few of director Chris Columbus's relatives also appear in the first two movies as extras.
Similarly Named Works: "Home Alone" is also the name of an unrelated public service video that shows viewers what to do if they're at home by themselves (i.e., if someone calls on the phone, don't say you're home alone, etc).
Part of this movie's central premise is that Kevin *enjoys* being alone and feels like as it is "his house," he must defend it. The cell phone idea assumes that Kevin even has access to a cell phone; many parents do not let children under the age of 12 have one.
According to director Chris Columbus, and early promotion posters, the original Home Alone music score was to be composed by Bruce Broughton, who ultimately got caught up with scoring The Rescuers Down Under, and was unavailable to score Home Alone.
Also, according to Columbus, John Hughes wanted to film Home Alone 2 and Home Alone 3 back-to-back, but 20th Century Fox declined to do so.
Hughes' original concept for Home Alone 3 was to be about Harry and Marv doing a Heel-Face Turn, moving to the suburbs, next door to each other, raising their own families, while Kevin does a Face-Heel Turn, and is released from jail, when he decided to exact revenge on Harry and Marv.
Sigourney Weaver was considered for the role of Kevin's forgetful mom, but didn't get it. Probably would have clashed with her protectiveness in Aliens anyway.
And if Home Alone 4 was successful? We would've had a TV series about it on ABC Family. Within the film, Kevin's parents didn't get back together in an earlier script. The ending was rewritten in case they ended up making the show.
In the commentary for the first film, Chris Columbus said that he had planned for Home Alone 3 to be filmed right after Home Alone 2, which would've starred Macaulay Culkin again (Though it is unknown if there would be any difference between the original idea of Home Alone 3 and the one starring Alex D. Linz).
According to AMC's Story Notes, Joe Pesci once said that his idea for a 3rd film would be Kevin lost in Hawaii, or a beach resort.
Daniel Stern refused to reprise his role as Marv in the fourth film, saying it was "An insult, total garbage." Day-um.