The Alta Stone Bag is a polyester platform that attaches to the legs of your tripod.  This can be used:
1. As a counterweight that provides additional stability when you're using a heavy camera/lens combination, or you're operating in windy conditions where a hanging object may be blown to create movement in the tripod.
2. As a "shelf" in the field to keep essential camera accessories, such as lens caps or filters, safe and accessible. When used as a shelf, there is a hook on the bottom of the stone bag so you can still attach additional weights. 
The bag is made of durable polyester and easily attaches to all tripod legs through hook-and-loop fasteners. You can easily fold it and store it in your camera bag.