To keep your hands dry throughout the climb, it's essential to have chalk handy. For bouldering, it's common practice to fasten the chalk bag around the waist with a strap. This allows easy access to the chalk during movement. In route climbing, the chalk bag is usually attached to the harness with a carabiner. This configuration keeps the chalk within easy reach while climbing the route. So, whether bouldering or climbing a route, it's important to have a practical system for carrying and accessing chalk while climbing.
The chalk bag should have an opening wide and deep enough to accommodate the whole hand, but not extend beyond the wrist. It's important to have an effective closure to prevent the chalk from dispersing into the bag. In addition, it can be handy to have a built-in reserve, such as a Tupperware-style compartment, for storing a spare bar of magnesia.
An expert tip is to tie the chalk bag around the waist with a cord or shoelace, rather than attaching it to the harness. This makes it easy to use as a block, or to slide along the waistband to move it from side to side. Be sure to fill the bag exclusively with magnesia and not talcum powder or flour, as these substances won't provide the same grip.
By following these recommendations, you'll have a practical and functional chalk bag for your climbing sessions.