Added a new property to items; isUsable.
Item's that CANNOT be equipped or have an otherwise useful effect should set this to false. This hides the "Use" button in the replace/discard/use menu when your inventory is full and avoids a weird looping issue:

Fill inventory.
Buy Hoverboard from Shekka.
Attempt to use Hoverboard from replace item menu.

The hoverboard use function was returning true, thus leaving the menu in place from the replace/discard/use trio of controls. In response, it's been reported as broken (and it's a very clear thing). I figure NOT having the button there to even tempt interaction is the best solution.