This could be quite easy to achieve with just a single listBox control plus a Text control for the caption. These controls would hide themselves upon losing focus or it would show itself and fill it's list as appropriate for the given gear type.
The listBox could reposition itself to either: overlap or align itself with the current gear slot when activated, depending on design.
The listBox could resize itself, both in width plus row count, to suit the current gear type and count. Given that some slots, like 'compass' would generally only have 1 item.