Our Pre-K group made fossil dough using flour, salt, and coffee. We put small dinosaurs inside the dough and let it dry overnight. The children had a great time pretending to be paleontologists while searching for the hidden "fossils".
1 cup used coffee grounds
1/2 cup cold coffee
1 cup flour
1/2 cup salt
Mix all ingredients together and knead until well mixed. This mixture will dry if left open to air. To keep soft, store in a plastic bag in the fridge.