It's hard to select a specific tool quickly with the mouse wheel being the only way to switch the tool being used, this increase in time to select the desired item may even get you killed sometimes (e.g. in a situation where the player needs healing or a weapon), and not because you didn't react quickly enough. My suggestion is to add a quickbar for the usable items and tools (tool quickbar), which could switch places with the building quickbar when a key is pressed.
Also, I don't see why a player would need to equip an item that is not an armor to use it, so with the addition of this quickbar, it would be a good time for the removal of the hand slot mechanic. The hand slot has a small balancing purpose, but it's mostly really annoying, most of the times the limitations it implies are not a balancing one (better combat, faster resource collection), but only a waste of time to switch which item is equipped before using it.