It is not safe to plug one power strip into another. This is called piggybacking or daisy chaining, and it creates an electrical fire hazard that could prove to be catastrophic.
Standard power strips should not be used in areas where they can get wet. This includes kitchens, bathrooms and garages that are not climate controlled. Specially designed power strips are available for damp spaces within the home as well as outside areas that are not protected from rain and other elements. A power strip for the garage should be hard wired and wall mounted by a professional electrician to ensure safety.