Do not leave empty space under the sink, especially in a small kitchen. With a rational approach, you can always place a lot of necessary things here. The main thing is to provide unhindered access to communications if necessary. Retractable or folding shelves, rails, different in configuration and filling of the storage system can be thought out in different ways. Much of the choice depends on the amount of free space and the shape of the wash itself. In the design, where the sink is framed by a table top, not only the side space, but also the top panel can be used for kitchen utensils, cleaning and detergents and other accessories. If desired, it is easy to use even the door. Take a look at the already implemented successful ideas, maybe some of them will become for you a guide to action.