@Michael_Ware - good to know. I’ll make sure I patch that, thank you for letting me know.
I don’t have any real appetite to make first join kits per world, as in vanilla Minecraft, you have one inventory for all worlds, and I see little use of having a first join kit per world if you have one inventory only. If you are using ProjectInventories, I’d actually suggest that @TrenTech should add initial inventories into there - I think that would be a better fit. I’ll more than happily work with him to achieve this if he wants some help.
Short term, depends on your permissions plugin and if it allows per-world permissions. I’d create a series of one time use kits for each world, and use your permissions plugin to restrict the permissions for each kit to a world using contexts (allow in one world, deny in all others). Then, instruct the player to redeem the kit when they first spawn in the world somehow.
I don’t know the specifics of how each permission plugin works, you should ask each of them for how to set world specific permissions.