A few of my favorites are:
Quick facial exfoliation:
Make a paste in the palm of your hand with baking soda and water, massage in circular motion all over face avoiding under eye area. Rinse with cool water and pat face dry.
Whiten you teeth:
Make a paste with hydrogen peroxide solution (just that stuff everyone has around) and baking soda in a little bowl, put it on your toothbrush and brush your teeth, rinse and spit.