Danno is right on (as usual). In fact , there is a story on use of toothpicks in one of the current magazines, I think it's Vintage Guitar, IIRC. One suggestion: try and get good and solid round hardwood toothpicks, not the cheap flat ones. Put it in with some wood glue. Let dry 24 hours. Carefully (with a razor or similar blade) trim off the extra toothpick sticking out of the hole, then replace the screw.
Bill, tgo