Clamps. Woodworking clamps are essential when building a project. They hold the components together while assembling them together, gluing them, during measuring, cutting et cetera. Be generous with the number of clamps you purchase because you will always need more than you think, and it gets difficult to assemble the project if you do not have enough clamps.
Another fine example of remodelling furniture and re-using what already exists in the house. The bookcase involves using your old kitchen cabinets, and building new shelves on top of them. The final product can also be used as an entertainment unit, housing a television, books and things of your interest along with ample storage to keep other utility objects.