Stretch! It will improve your flexibility, of course—but it will also make you stronger.
The Hippie
Pretend your head weighs 500 pounds, and let it pull you down. Bend one knee and hold for 15 seconds, then change legs.
The Pecs Flex
As you lift your hands as high as possible, squeeze your shoulder blades together and open your chest.
The Leaning Tower
Try to elongate your body by creating the greatest amount of distance possible between your left pinkie and your left heel. Hold for 15 seconds, then switch sides.