Make use of every last ounce of your body wash or shampoo.

Im sure some form of this has been said on here before but when you're almost "out" of your body wash or shampoo (nothing is coming out when you squeeze it) fill the bottle with water about 1/4 or even 1/2 way. Then shake it up. You'll be surprised at how much is actually left that is just stuck to the inside of the bottle.