Hey, thanks for the feedback!
>Is there a way to rearrange them
Right now you can either assign a different item to a slot, or do it twice to clear the slot. I don't clear slots after all the items have been used on purpose, so you don't have to reassign them if you find new ones.
>I think that part is endless?
Yes, it is currently endless.
Anyway, your points are valid. Corrections / fixes / changes are planned for future versions.