Here's a few.
-Coin stamps- Show different ways to make 1.00
-Fruit loops- Generic brand tends to have bigger holes. Make a necklace showing groups of 10.
-Race to 100. Give out a hundred chart and dice. Take turns rolling dice and coloring in that many spaces. First one to 100 wins.
-Race to Zero- Start at 100 and subtract when rolling dice.
-Read the Wolf's Chicken Stew. Then draw and write what else the wolf can bring. (In the story he brings 100 of things!)
-Draw what you think you will look like when you are 100.
Read If You Lived 100 Years Ago. Talk about past and how far things have come. Then they write and draw what they think world will be like in 100 years.
-How would you spend 100 dollars?
-If you have 100 piece puzzles, group them and see how long it takes to complete puzzle.
-Take 100 steps, how far can you get?
-Estimation. Take 3 different size jars and fill one w/ more than 100, one with less than 100 and one exactly 100. Kids have to estimate which is which. ( I usually use candies that are diff. sizes - MIke & Ike's, jellybeans, M&M's, etc.)
-100 of some kind of snack. Discuss how to divide equally with class.
I am jelous that you are at the 100th day.
We are at 78. I have some more literacy ideas but my file is at school.
Hope this helps! I love the 100th day.