Adaptation Overdosed: Let's see, 16 films, a TV series, countless re-imaginings and sequels in book and motion picture... That's not even getting started on the anime, video games and Visual Novels!
Beam Me Up, Scotty!: Carroll never refers to the Hatter as the Mad Hatter. Nor does the White Rabbit ever say "I'm late! I'm late! For a very important date!" except in the Disney version. A minor case appears in Jabberwocky. The birdlike creatures in the first stanza are borogoves, but many misread it as borogroves, which isn't helped by some printings getting this wrong, too.
The Wasp in a Wig. Some editions actually publish this chapter in its proper place at the end of Chapter 8 in Through the Looking Glass.
Carroll had originally intended the illustration of the Jabberwock to be the frontispiece for Through the Looking Glass, but he worried that it might be too frightening for children; he requested feedback from some parents he knew, and eventually decided to move it to the second chapter (where the poem appears) and use a picture of Alice with the Knight as a frontispiece.
Word of God: According to Lewis Carroll, Alice's canon surname is Pleasance (from Alice Pleasance Liddell).
The members of the boating party that first heard Carroll's tale show up in the Caucus Race; Alice's sisters Edith and Lorina, are inserted as the Eaglet and Lory, respectively. Rev Robinson Duckworth is the Duck and Carroll himself is the Dodo.
Alice and her sisters appear again as Elsie, Lacie, and Tillie in the Dormouse's story. Elsie (L.C.) is Lorina (middle name Charlotte), Tillie is Edith (nickname Matilda), and Lacie is an anagram of Alice.
Alice's two other, lesser known sisters (Rhoda and Violet) make appearances in the second book, as the rose and the violet in the talking flower garden. The mouse who gives the "dry lecture" and the Red Queen were seemingly based off of Alice's governess. The Queen of Hearts and the Duchess were seemingly caricatures of Queen Victoria and her mother respectively.
Throw It In!: An unintentional Funny Background Event on the DVD: the gavel head breaks and flies off (violently!) when the Queen of Hearts tries to end the Mad Hatter's and March Hare's testimony. Cue some quick improvisation from both the King and Queen, who initially aren't sure where the gavel head even is, along with mimed amusement from the Hatter once he notices what's happening.
Not to mention the fact that one of the Tweedles is played by Robbie "Rubeus Hagrid" Coltraine.
The 1985 version also features a lot of names in the cast, like Sammy Davis Jr as the Caterpillar, Telly Savalas as the Cheshire Cat, Carol Channing as the White Queen, Roddy McDowall as the March Hare, and Ringo Starr as the Mock Turtle.
A 1933 version includes W.C. Fields as Humpty Dumpty, Cary Grant as the Mock Turtle and Gary Cooper as the White Knight, among other stars.
The 1966 version for the BBC is full of well-known British actors and comedians, including Sir John Gielgud, Peter Sellers, Leo McKern, Alan Bennett, Peter Cook, and Sir Michael Redgrave.
Dawson Casting: Alice is pre-pubescent in the books but most TV and movie adaptations depict her as a teenager or twenty-something (e.g. Fiona Fullerton). The few exceptions are 12-year old Sarah Sutton (UK) in 1974, 9-year-old Natalie Gregory (USA) in 1985 and Krystina Kohoutova (Czech Republic) in 1988). May Clark, the first actress to portray Alice in film, was 14 at the time (1903).
Kate Beckinsale plays Alice in a 1998 version of Through the Looking-Glass. It's interesting to note that the film starts out with Beckinsale reading the story to her daughter and that when she becomes Alice, she is "seven and a half exactly".
Janet Waldo, a.k.a. Judy Jetson, was 42 when she voiced Alice in the Hanna-Barbera version. Of course, adults voicing children is very common in the voice acting industry and the character was drawn as a preteen, but it still might make her the oldest person to play Alice.