You can always work with single clicks doing multiple different things depending on the conditions.
Example:
You have an inventory with a couple random items. Left click can equip any clicked on item. And a button or clickable sprite that toggles on Arrange. Now click on an item and the item follows your mouse until you click again. If you click over another inventory slot they will swap places, if you click over a non inventory slot it goes back to its original location.
The toggle can be as simple as a Global variable Arrange. When Clicked it sets Arrange to True.
Whenever you click an item in your inventory and (Invert)Arrange is True then Equip
Whenever you click an item in your inventory and Arrange is True then Equipment follows mouse