One of my favorite math activities to do each year is "puzzle piece counting." You buy a puzzle with 100 pieces. Put it together before the school year begins, and write the numbers 1-100 on the back of them with a tiny sharpie. Then add pieces of magnetic tape to them. Every day of school, add a piece to the puzzle.
In the picture below you can see that we have one piece missing since today was our 99th day of school. Tomorrow we finally get to add the last piece!
This one is great for talking about numbers beyond 100. After the 100th day, kids seem to think that school will be over or they get to move to the next grade. I love using this one as a teaching tool for three digit numbers.
I selected the dollar bill and penny because they were math related. I purchased them at the Target-Dollar Spot, and they have been a wonderful addition to our calendar math. It's so simple and easy, but the kids get so excited when they see the puzzle growing larger and larger. I think I'm going to try to find a puzzle with 75-80 pieces to use for the remainder of the school year.