Lo-Fi Games

I see youtubers stacking items in their inventories and im trying to figure out how to stack items. I cant figure it out. i have tried right clicking, left clicking, and holding right click to see if theres an option.. is stacking disabled or something? im running on newest version of kenshi

you can stack items in backpacks

Specifically, in traders backpacks. Items do not stack in your inventory, if you have a traders backpack equipped you can right click the items in your inventory and it will transfer them into the backpack and stack them with any identical items(some swords are almost exactly the same in icon appearance but differ slightly).