I recently had a little sensory play spurt that was a lot of fun while it lasted. We played with spaghetti, cloud dough, Ivory soap, beans, and rice. But the most unusual thing we tried was eggshells. The idea was from Play Create Explore where you can find all sorts of fun sensory play.
It only took a few days of saving and washing the eggshells (with soap and hot water) to come up with a nice bowl full. We eat a lot of eggs.
An unplanned and interesting dimension to this experiment was that some of the eggs were home-grown (brown) and some were store-bought (white). We found that the store-bought eggshells were thinner and easier to crush than the thicker home-grown ones.
We also found that the edges are sharp. This is probably not appropriate work for very small people.