That last little bit of peanut butter or mayo out of a jar.
Use half a junk-mail envelope to write your grocery list and hold your coupons.
Cut the tube open--makeup, toothpaste, whatever (I recently did this with some BB Creme and so far got four more applications from the "empty" tube! There is still enough makeup in there to last at least one or two more days. Normally I would have just tossed it, but I do my makeup at work before start time and I had ran out. Now that I know how much is left in there, I'll make cutting it open a habit.)
Reuse a sandwich bag that had been used for crackers.
Use the back side of a piece of paper to make a list or as scratch paper.
Come back and share what it was you were able to squeeze one final use out of.