I teach 2nd grade and our 100th day of school is on January 25th, 2011. I made these fake 100 dollar bills by printing the image for a $100 bill on green cardstock, then covering up Benjamin Franklin's face with a photo I took of each of the kiddos.
On the back is a sticker that says, "It's the 100th day of school and you're worth a hundred bucks! Love, Mrs. Berenter January 25th, 2011."
I added some clear lanyard after I punched a hole and will be putting them on the zippers on their backpacks!
When my youngest daughter was in 1st grade, her teacher made these for her kids and I LOVED the idea, so naturally I stole it! Teachers are secretly great thieves, but we also try to give credit to someone else if it's not our idea! :-)
P.S. I blurred their faces to protect their identities.