Grasp the strap with one hand and push the pack section away with your other hand to create an opening. Lower the sling pack over your head so the pack is centered on your back and the strap runs over one shoulder and under your arm on the opposite side of your body.
Locate the adjustment loop, clip or buckle on your sling pack. It is typically near the bottom of the strap. Pull the adjustable section of the strap to loosen or tighten the pack until the base of the pack hits near your waistline and there is just enough slack to comfortably slide your hand between the strap and your chest.
Remove the sling pack by grabbing the strap with one hand between your sternum and shoulder. Pull the strap over your head and place the pack on a flat surface. Some packs may have a hook and loop attachment in the center that lets you disengage from a heavy load without raising it over your head.
Fill the sling pack with needed items. Zip it closed and put the pack on to check for fit. Adjust as needed.