Seven Seas has an unreliable track record with translating bonus material. This is the most comprehensive collection you'll find of ILTV bonus material with no official translation. Some of these are manga, some not. Some of these are posted elsewhere, but non-manga titles in particular... Aside from others' uploads, probably not.
The presented titles are generally unofficial.
MelonBooks Tankoubon (Manga) Leaflets
Volume: Tanko #1 (MelonBooks print version)
Rae and Claire have gone out for Melon Soda.
Volume: Tanko #2 (MelonBooks print version)
Tea Time!
Volume: Tanko #3 (MelonBooks print version)
Gotta love a new look.
Volume: Tanko #4 (MelonBooks print version)
I have one question for you. What would it look like if Lene was a student at the Royal Academy?
Volume: Tanko #5 (MelonBooks print version)
As LN3+ readers should know, above is the in-universe name for Christmas. Claire and Manaria are out just enjoying the night, and...Rae might just keeping an eye on Manaria.
Volume: Tanko #6 (MelonBooks print version)
Rae and Claire are in Rae's world, visiting a festival. Claire wants a goldfish.
Volume: Tanko #7 (MelonBooks print version)
THE TIME HATH COME for Rae to have a fantastical little dream.
Volume: Tanko #8 (MelonBooks print version)
Rae's organized a meetup with Misha and Lilly, but she's nowhere to be found.
Volume: Tanko #9 (MelonBooks print version)
The seasons are changing, the leaves are falling... Just like how Lilly's fallen for Rae.
Volume: Tanko #10 (MelonBooks print version)
Lilly's trying out a cool new style to try and get Rae's attention.
Volume: Tanko #11 (MelonBooks print version)
Rae and Claire go on a visit to Japan to see the wonders of the big city!
Volume: Tanko #12 (MelonBooks print version)
ILTV but animal crossing
Other Manga
Origin: ILTV JPN Blu-ray BOX
A short bonus comic included with the Japanese release of the ILTV Season 1 Blu-ray.
Origin: Tanko #6 (DMM Books digital version)
A brief bonus comic that answers the question, "What if pre-merge Rae met Claire?"
A collection of single-page bonus comics that was available at the 2023 Animate fair.
Origin: ILTV Light Novels' Revolution Edition Vol. 2
Written Shorts
[MAY CONTAIN POST-MANGA SPOILERS!] One might remember that Rae mentions having written a fanfic about Claire falling from grace and climbing her way back. This is that fic.
[MAY CONTAIN POST-MANGA SPOILERS!] This is one of many bonus chapters set between Acts 1 and 2. I guess they just...forgot this one? In any case, the title is self-explanatory. They get colds!
Other
Known exclusions
Vol. 1-6 Story cards
Revolution Edition bonus leaflets
BD-BOX written bonus story "Vow"