I do not have scripting knowledge so I am unaware of whether I am asking for something simple, or very complex.
But there are many kind of objects that can use such a tool to stack together. I have noticed there are several different types of:
Tanglefoot bags
Arrows of various kinds (Ice arrows, flame arrows, etc.)
Choking powders/ goblin stinkbombs / flash powders
I'm sure there are other stackable items I am unaware of. Just thought it'd be handy to have a tool like that. Especially for the arrows. Stacking special arrows would prevent having to swap out small stacks during a fight, since the stacks you equip will be bigger.