Water Street runs right through downtown St Andrews, as the name suggests, right along the water. They have several shops featuring everything you could possibly want from blown glass, pottery and other local crafts to name brand clothes.
Water Street is considered a historic district, so none of the merchants have been allowed to demolish the old buildings to make way for new ones, so you still have the homes that are 150 years old doubling as things like a stained glass shop.
Water St isn't very long, so you can cover both sides in about 3 hours. It's definitly a nice way to spend an afternoon.