By cutting an "X" through a tennis ball and stick a broom stick through it, you've now created a wood floor scuff remover that erases black skid marks from no wax floors. Check it out, someone even applied for a patent for it.
And if you're in a pinch for a sink plunger, you can use a halved tennis ball to create a small suction cup device. Just press it over the opening (which needs to be smaller in diameter than the tennis ball itself), and press to agitate the obstruction. Game, set, match...you win.