Baking soda - great mild abrasive, works better than Comet on bathtub scum.
Vinegar - cleans well, removes buildup, works well to clean up limescale and calcium build up (like CLR)
Rubbing alcohol - diluted, cleans up yucky messes and dries quickly (like cat upchuck)'
Baking soda AND vinegar - clears out drains like drano!