Panning for Gold - collect & paint rocks & hide them in sand. use sifters to 'pan for gold' - from Mess for Less (",) sensory table
I like how this activity is potentially messy but definitely open ended and no final product can be predetermined. It would be a great physical art activity where the children can see how their body's movement determines the mark that they can make. I chose to put this in the outdoor category because the more space for this activity, the better, in my opinion.