In a small bathroom, less is always more. If you include a vanity, you will probably need to choose a very small unit. Depending on your needs, you can choose the style (cabinet or drawers or a combination) that is most suited to your needs. Recessed medicine cabinets (set into the wall, with an unframed mirror) are ideal in small bathrooms.
Most remodelers tend to think of a single medicine cabinet over the sink. But with a little creativity, you can use additional medicine cabinets in other places in the small bathroom to provide both space and the light-reflecting property of the mirror to make the room look larger. For example, a larger medicine cabinet placed in a wall at one end of or behind a tub is a great place to store soaps, lotions, bubble bath, wash cloths and even towels. All the items needed for the bath can be in close proximity yet out of sight.