My kids love watermelon and can eat a lot of it, but even so, the four of us have a hard time getting through a full-sized watermelon by ourselves. I recently discovered the perfect use for leftover watermelon:
It doesn't take much time or effort--crush up cubed watermelon in a bowl or cocktail shaker (using a muddler, a large spoon, a potato masher--whatever!) Strain the resulting watermelon slush through a mesh strainer. Voila! My son enjoyed his juice straight up, while my husband and I added a squeeze of lime and a shot of cachaca (a Brazilian spirit made from sugar cane--I bet vodka or rum would also be excellent). A perfect late-summer drink!