As a compulsive organiser, I like to move stacks of items around. In the midpoint of the game, some of your goodies will have stacks in the hundreds.
Could you please add a "split stack" option?
Split stack mechanics
A very popular implementation is that right-clicking a stack opens a window with a slider. Moving the mouse whilst holding right-click adjusts the split point for the stack, with the amount shown on each side. Users can also let go of right mouse and drag the slider manually. Some games also add buttons to add or remove 1/5/10 on either side, or make the numbers directly editable.