We made gak! Or whatever you call it.

Now this was fun! Messy, messy fun. To make this you need cornstarch and water. A bowl, some food coloring and patience are great to have too. First, I had K squirt some food coloring into a water bottle and shake it up. (That alone was so fun we had to do that another day with all the different colors.) Then she measured out some cornstarch and poured it into the bowl. After that, she poured the water on top. We mixed with our hands until we liked the consistency. We had to go back and add water, then add cornstarch, etc. etc.
This stuff feels so cool. K loved watching it slip through her fingers. She played for so long. Then she got up and said "bath." We had to laugh at that.
Another great thing about this activity is that if you just let this water evaporate, you can go back and use the cornstarch again. That's why I do this in a plastic shoebox with a lid.