With two boards, you can turn a shelf into a wine rack. Use a space that is square, deep enough to hold bottles on their sides, and at least 14 inches tall and wide. Measure depth and diagonal distance between corners; cut two 1-by-12-inch boards to those dimensions, and sand to fit, if necessary. Notch middle of each piece at 90 degrees: Use a pencil and speed square to mark wood, and a jigsaw to make a 3/4-inch-wide notch that stops at the center. Bisect pieces at notched points to make a three-dimensional X. Paint to match shelves.