If you look at the Calendar you can see which volumes of books are being translated now and so are available to members: https://j-novel.club/calendar
There will also be some volumes that have finished being translated recently and do not yet require you to purchase them: https://forums.j-novel.club/topic/534/expiring-volumes-light-novels/342?page=18
From the expiring topic, Expiring September 16th, 2024:
Ongoing series list:
VTuber Legend Vol. 7
Campfire Cooking Vol. 15
Management of a Novice Alchemist Vol. 2
Misfit of Demon King Academy Vol. 7
I Parry Everything Vol. 6
Knight's & Magic Vol. 4
Peddler in Another World Vol. 8
Private Tutorto the Duke's Daughter Vol. 13
Taking My Reincarnation One Step Vol. 6
Zilbagias the Demon Prince Vol. 2
After-School Dungeon Diver Vol. 3
Black Summoner Vol. 18
Record of Wortenia War Vol. 25
Holmes of Kyoto Vol. 19
Seirei Gensouki Vol. 25
Enough with This Slow Life Vol. 7
Welcome to Japan, Ms. Elf! Vol. 9
Rebuild World Vol. 5
Min-Maxing my TRPG Vol. 9 Canto I
Goodbye, Overtime! Vol. 2
The Reincarnation of the Strongest Exorcist in Another World Vol. 1
Invincible Summoner Who Crawled Up from Level 1 Vol. 2
A Surprisingly Happy Engagement for the Slime Duke and the Fallen Noble Lady Vol. 2
DUNGEON DIVE Vol. 8
The Crown of Rutile Quartz Vol. 2
Cooking with Wild Game Vol. 25
Earl and Fairy Vol. 7
Tearmoon Empire Vol. 13
DUNGEON DIVE Vol. 9
Ascendance of a Bookworm Part 5 Vol. 12
Blade & Bastard Vol. 4
The volume 1's are these:
The Blessing of Liefe Vol. 1
The Fake Hero Crashes the Party Vol. 1
The Royal Hostage Has Vanished Vol. 1
The Hero and the Sage, Reincarnated and Engaged Vol. 1
Dagashi-ya Yahagi Vol. 1
The Poison King Vol. 1
If you like to be able to read more than the bite-sized samples that Amazon, etc. give you for their ebooks then the membership is a great way to read an entire volume of a series before deciding if you want to buy it.