Here are some of the activities I have done in the past with my Kinders through 4th graders.
The students counted out 100 ice cubes and we made predictions as to when they would all melt.
Another activity my Kinders did was to play a rolling and counting dice game. They had to roll the die and then color that many squares. The first team to hit 100 won! (For the second round we played that the person on the team to color the 100th square won!) My Kinders LOVED this!
Another activity that the Kinders really enjoyed was to guess how long 100 seconds was. I had all of the students put their heads down. When they thought 100 seconds had gone by, they were supposed to QUIETLY put their head up. Obviously these little ones had no idea how long it was! After about 10 seconds roughly half of the class put their heads up... So then we talked about how long it really was and tried it again. I felt it just helped make them more aware of time...
One activity that I have done at EVERY grade level is to have them do 100 seconds worth of different exercises or 10 of each different exercise all the way to 100. For example - jumping jacks, sit ups, push ups, etc. The students always giggle the whole time, but it is a GREAT way to burn off some of that energy from a day that doesn't follow the normal routine.
The last activity for the day for my Kinders was to string a cereal necklace with 100 pieces of honeynut cheerios. (In hindsight I would have used fruit loops, as they are bigger - oh the things you learn your first year of teaching Kinders!) Either way, the students really enjoyed it!
One of my favorite snacks I brought was stick preztels, oval crackers, and cheese. The 3rd/4th graders had a blast spelling out 100 using the pretzel sticks as 1's and the oval crackers as 0's. :)
One of my coworkers did a 100 minutes of reading activity with her upper elementary/middle schoolers. The students LOVED it!
I have always loved the writing/art activity where teachers have the students make a picture of what they would look like at 100 years old and then write about it. One of my former coworkers even went to far as to let her students dress up as though they are 100 years old on the 100th day of school. That is ALWAYS a HUGE hit!! :)
One more FREE resource. I have worked in some schools where student attendance can be a real issue. So in 2011 I created a basic little certificate for any students who had perfect attendance for all 100 days. We had an elementary assembly (only 100 students) and had our principal present them. You can get your FREE copy here!
I know there are other activities out there that I've done, so maybe there will be another 100th day post as that day draws nearer. But - in the meantime - check out my Pinterest board where I have a few 100th Day of School items posted. I plan to add to it regularly, so make sure to check it out!
Happy 100th Day!