According to Jacco, this is the best chalk bag on the market.

The Cocoon Clic-Clac chalk bag comes with a unique, snap-closure opening system, making it easy to open with one hand, even while you're climbing! Its metal rim springs open and shut, securely sealing the bag, and stays wide open for hassle-free access to your chalk. It's perfect for climbers seeking a reliable, efficient way to reach their chalk without interrupting their climbs.