I have been playing the game for a few days, and like it a lot. I have found that it is cumbersome to equip and unequip soldiers, especially when adding lots of little things like grenades and clips, because each item must be dragged onto a valid slot. I suggest that simply right clicking on an item will unequip the item when it is equipped. When it isn't yet equipped, right clicking will put the item into a reasonable default location.
For example, if no weapons are held in a soldiers hands, right clicking on a weapon will put the weapon in their hands. If the soldier already holds a weapon, and a weapon is clicked on the weapon will be placed in the holster if it will fit and in the backpack otherwise. Clips and grenades will be put in the belt or some other suitable place.