This was my outfit for the day -- a jean jacket made with 100 bows covering it (just like Miss Bindergarten!). My mom made it for me!
(I can't get it to rotate...sorry!)
We also made 100 Fruit Loop necklaces. These necklaces were not hard to make. I gave each child a ten frame and they made a set of 10 Fruit Loops of one color. Then they put this set on their yarn which was taped to to table. The other other end of the yarn was wrapped with Scotch tape to make it easier to string the Fruit Loops.
I hope this will give you some inspiration if your 100th day is coming up!