One of my all time favorite activities for the 100th day of school is the Hershey Kiss Hunt. Basically I purchase a couple of backs of Hershey Kisses and some circle dot stickers. I number the stickers one to one hundred and then stick them on the bottom of the Hershey Kisses. While the children are at special area, I hide them around the room (like Easter Eggs for an Egg Hunt).
When the children return, I set out the hundred chart. When each child finds a Hershey Kiss, he/she places it on the hundred chart until all the candies are found. Once all the candies are located, we divide up the Kisses evenly.
The kids LOVE this activity!