This is going to be a big one, but I figured I'd collate 1st appearances of Across the Spider-Verse characters that people may want notated in key notes. Vague spoilers ahead.
More than likely a lot of these won't warrant a key notation but, at the very least, you'll have this post to point to when people ask about random alternate universe Spider-Men
I've tried to order them by 'key note likelihood', but, of course, I am not the authority on that
Vault of Spiders #1 (12/18)
1st Appearance of Spider-Byte (Margo)
[She plays a not-insignificant role in the movie, managing the Go-Home machine and having a few scenes dedicated to her]
Spider-Geddon #0 (11/18)
1st Appearance of Insomniac Spider-Man in comics
[He only has a brief cameo in the movie, but he is also the star of a major video game & several other comics]
LEGO Marvel Super-Heroes #5 (08/12)
1st Appearance of LEGO Spider-Man
[There are no copies of this on the CGC Census, I believe it was packed in with the LEGO set 6873: Spider-Man's Doc Ock Ambush, The character of LEGO Spider-Man does get an entire section of the movie dedicated to him, but I understand that this iteration of the character might not justify his own key note]
Spider-Man 2099 meets Spider-Man #nn (11/95)
1st Appearance of Spider-Man 2211 (Max Borne)
[This Spider-Man gets his own lines during the chase scene, and has appeared in a few non-Spider-Verse comics]
Spider-Verse #3 (02/20)
Appearance of Sun-Spider (Charlotte Webber) in pin-up
Spider-Verse #6 (05/20)
1st Cameo Appearance of Sun-Spider (Charlotte Webber)
Edge of Spider-Verse #4 (11/22)
1st Full Appearance of Sun-Spider (Charlotte Webber)
[These probably don't all need key notes, but the character is adapted into the movie, getting her own lines during the chase]
Edge of Spider-Verse #1 (10/22)
1st Appearance of Spider-Rex (Pter Parker)
[This Spider is given his own fight scene, being called out as one of the 'weirder' spiders by Miles]
Spider-Island: I Love New York City #1 (11/11)
1st Appearance of Spider-Cat
[They are the only Spider without any lines that got their own poster, which may or may not justify the key note]
Amazing Spider-Man #12 (07/16)
1st Full Appearance of Web-Slinger (Patrick O'Hara)
[Technically appears in cameo in a crowd shot in Amazing Spider-Man #9 (05/16) & his name is not revealed as Web-Slinger / Patrick O'Hara until Spider-Verse #4 (03/20), He might justify a key note as he exchanges words with Miles both before and during the chase scene]