Have a rather large collection of adjustable wrenches, c-clamps or odd-shaped screw clamps laying around the workshop? You can store them neatly side by side just by tightening up their jaws on the edge or lip of a shelf that is out of the way. They will take up very little room and will always be easy to spot and retrieve. If the ceiling joists are accessible in your shop, they also can be used for clamp-on storage.
To store a carpenter’s square, nail either a 13-in. or 22-in. length of tongue-and-groove flooring to your shop wall, groove side up. Then, to hang your square, just drop one leg of the square into the groove of the flooring piece. The length depends on which leg you want to be horizontal.