4. Third Hand
A pair of mini locking pliers is a great substitute for a helper when you need to tighten fasteners penetrating bulkheads, decks or other areas where you can't reach around the other side to hold the nut. Lock the pliers on the nut, and then apply a wrench or screwdriver to the fastener's head. The nut will spin initially, but after a half turn or so, the locking pliers will inevitably encounter an obstruction, preventing the nut from turning and allowing you to sock the bolt down tight.