I'd love to be able to move objects between bags using only the keyboard, as I find it very hard to drag and drop on my computer without screwing up (go laptops!)
My suggestion for implementation: designate a key - v perhaps? - that, while over an item in your bag, marks the item, and then, when over an empty space, moves the marked item to that space. If you press v over another item, it flags that one instead, and if you press v in a space the highlighted item can't be moved to (ie in a toolbox, or trying to put a bag in a bag), nothing happens, or something flashes red, or something. Maybe the "nope" sounds is played.
Of course, I'll be happy with whatever way is used to implement it.