We use a lot of whiteboard markers; we have a big whiteboard we use for planning (which often overflows onto the window next to it), we have some 1 ft² plexiglass sheets we use to label things, and so on. And some of us aren't so great at remembering to put the caps back up.

Fortunately, one of the teacher at the high school showed us a sweet trick. White board markers are just plastic tubes, sealed at one end, with a sponge soaked in ink, and a cap on the other end (or at least, there's supposed to be a cap). When a whiteboard marker dries out there's often still ink in the main part of the sponge, but you can't use it because the end you care about is dry. But, by using centrifugal force to get the ink to flow to the cap end by 1) taping a string on the sealed end and 2) whirling it around.

But make sure you have the cap on when you do this, and don't swing too fast (or too long?) because you only want the ink to reach the tip of the sponge and there's nothing preventing it from going past the end and off onto a great adventure, and your hands.