How about 2 new separate item menus?
The first one (the one we already have) could be reserved for weapons/useable items
The second one could be reserved for Equipment (select one of them, click to equip, click again to unequip. Equipment will remain equiped even when several are equiped at once, etc.). It will automatically unequip when the item is dropped, of course.
The third one would be a Vehicle Weapons/Measures menu, which would replace the regular on-foot weapons/useables menu and provide you with vehicle weapons instead. A tank, example, could have 3 measures: Main howitzer cannon, a machine-gun, and finally a smock screen projector.
