The bartender spitting into Homer's drink before he forgets everything is a reference to the movie "Memento".
As Homer grows fast-forward, the music video Everyday by Carly Comando plays.
At the end of the "Picture A Day for 39 Years" scene, there's a YouTube replay parody (resembling the version from the time the episode was made/aired) with the exact 50 seconds listed as how long the scene lasts which is true. The bottom of the video list is a video of "Kitten Smokes on Toilet" which has incredibly more views than Homer's.
While falling, Homer's life flashes before his eyes. The scene is a parody on the popular YouTube video by Noah Kalina which features a fast montage of thousands of pictures of him spanning a period of six years all played sequentially.
When Chief Wiggum asks Homer who Jack the Ripper was, Homer says it is the queen's private surgeon. Referencing theories about the murderer and that he was connected to the royal family which was why he wasn't caught.
Julio's revealed to originally from Costa Rica, when he is with a group of Mexicans beating up Krusty the Clown for his offensive jokes towards Hispanic-Americans.
A character who resembles Troy McClure can be seen among the Mexicans beating Krusty up.
This is the last episode to air in 2007.
This is the second Homer tries to jump off the only bridge out of town, the first being Homer's Odyssey, but in that episode he didn't succeed in jumping.
In the "Picture a day for 39 years" it reveals that Homer failed the second grade. Homer would be smart at that time from the Simpsons gene shown in "Lisa the Simpson". This explains the Simpsons gene doesn't affect the whole series.
During "Picture A Day for 39 Years" part, Homer makes a Pyramid, The Taj Mahal, and The Brooklyn Bridgeout of "Duff" beer cans.
In the "Picture A Day for 39 Years", there are versions of Homer from previous episodes:
Other pictures include him dressed up various ways not from episodes, for example, Homer was dressed as Santa, but probably it came from "'Tis the Fifteenth Season", because Homer was dressed as Santa there.
One of the snow statues in the sledding scene was the Kool Aid guy from Family Guy.
While Homer is going through all of his memories (basically screenshots from older episodes), the following episodes are seen:
"Tennis The Menace" (Homer with Marge, Lenny and Carl)
"Home Sweet Homediddly-Dum-Doodily" (Krabappel talking to Nelson on picture day)
"The Call of the Simpsons" (Homer as Bigfoot, when the family arrive at the park, Homer with honey and bees in his mouth, Bart lamenting over Homer getting tranquilized, Homer naked, Homer as Bigfoot with Bart, Homer and Marge with Cowboy Bob)
"The Crepes of Wrath" (Ugolin and Bart on the motorcycle, Homer laying on the couch)
"The Telltale Head" (Bart and Homer talking to the mob, Bart in Sunday School, Homer's face when saying "Catch it!" while listening to football, Bart taking off his church clothes, Marge's face when yelling "Now move it!",)
"Viva Ned Flanders" (Amber and Ginger with Gunter and Ernst)
"Behind the Laughter" (The Simpsons greeting everyone, the Fox Broadcasting door, the Simpsons in the recording booth, roses falling on The Simpsons)
"Itchy & Scratchy & Marge" (Homer talking to his family)
"HOMR" (Moe doing Homer's brain surgery)
"Das Bus" (Bart and Martin eating)
"Sunday, Cruddy Sunday" (Homer, Bart, Wally Kogen and the boys in Rupert Murdoch's skybox)
"Homerazzi" (Homer taking pictures of various celebrities at Rainier Wolfcastle's wedding, Homer at the celebrity dance club later in the episode)
"Treehouse of Horror" (Serak the Preparer putting in salt, Homer going insane in "Bad Dream House", Serak with Homer and Marge)
"Krusty Gets Busted" (Krusty lined up with a bunch of clowns)
"Treehouse of Horror VI" (Willie as the giant spider and in Martin's dream)
"How I Spent My Strummer Vacation" (When Otto, Apu, Wiggum, and Homer arrive)
"Homer Loves Flanders" (Ned with his gun)
"Lisa's Pony" (Lisa on her pony)
"Little Big Girl" (Bart and Darcy meet, the family's, the wedding preacher's, and Darcy and her dad's "Awww" reaction to Darcy's mom having another baby)
"Homer's Night Out" (Homer with Gulliver Dark)
"Grampa vs. Sexual Inadequacy" (the farm where Homer lived as a child)
"D'oh-in' in the Wind" (the mural by Mona painted for Homer)
"Mother Simpson" (Mona leaving Abe and young Homer)
"The Way We Was" (Homer and Marge together at high school)
"Bart Gets an Elephant" (Bart, Snowball II and Santa's Little Helper seeing Stampy for the first time)
"Moaning Lisa" (Lisa sadly looking at herself in the bathroom mirror)
"A Fish Called Selma" (Selma and Troy McClure's wedding)
"Some Enchanted Evening" (Marge roaring at the kids)
"Two Cars in Every Garage and Three Eyes on Every Fish" (Mr. Burns about to spit out a piece of Blinky)
"Burns' Heir" (Martin auditioning for Mr. Burns)
"The Italian Bob" (Sideshow Bob introducing Francesca and Gino Terwilliger to the Simpsons, the Simpsons on the plane)
"The Way We Weren't" (Homer and Marge's first kiss)
"Mr. Plow" (The Mr. Plow commercial)
"Bart the General" (Homer and Bart in the kitchen during the beginning of Act 1)
"Funeral for a Fiend" (The Simpsons being booed at Sideshow Bob's funeral, Sideshow Bob and his family in jail, the Wes Doobner commercial)
"Treehouse of Horror IV" (The family saying "Happy Halloween, everyone!" at the end of "Bart Simpson's Dracula")
"Lisa the Vegetarian" (Homer, Marge and Bart singing "You don't win friends with salad")
"Treehouse of Horror XII" (The family screaming when Mr. Burns scares them in the opening)
Considering the fact that screenshots from flashforward, Treehouse of Horror, and other non-canon episodes appear, this episode may be non-canon, but only to a degree.
Unless the entire show was dreamed by either one of the Simpson family (Homer, Marge, Lisa, Bart, or Maggie, but more likely Homer), this episode would be the only episode to take place in a nonspecific canon.
In Homer's memories, he was shown diving naked near a cliff, but he couldn't have remembered that because it was in a dream that Marge had in church. There is also another memory from Martin's dream from Treehouse of Horror VI. It is possible that Homer imagined them separately.
Through the first two acts, as well as during Homer's cascade, it is winter in Springfield and the snow falls in many scenes, if not it is on the ground. In the party boat scene, all of a sudden there is no precipitation and everyone is dressed lightly as if it were a warm, pleasant night (not to mention it would be weird to be partying on a ship's deck in cold weather).
After Homer jumped on the boat, you can see that the boat is far away from the bridge.