Here are a few ideas from Make Magazine, Radio Shack, Sparkfun, Adafruit, and Instructables which would make fun projects to work on during open shop. If none of these strike your fancy, there are tons more where they came from!!
Build an awesome soldering stand.
Drawdio is a simple electronic sound synthesizer built onto a pencil!
Circuit on a breadboard
This would be a fun project to display at Roundup or the fair.