Animelover07
Instead of item that grant limitless stamina, can't you pick a power? Let's say, "star radiation absorbing kryptonian, mortal body".. So it can absorb sunlight and star light for you, adding it to your mortal body permanently,strengthening it.. Item can be stolen after all... Or get an item, big item that hard to steal. Then the item maybe could absorb sunlight like the solar charger panel, and then you can absorb it after night to have a balance increase of body strength.. *Sorry, I didn't know how to word it better.. *