A bolt pouch allows a member to carry more bolts. It can be purchased for 1,500 gp from Hirko, who is located in Keldagrim, eastern side of the river. (You must talk to him and ask about ammo, the pouch is not found in his trade option)
The bolt pouch menu when left-clicked
Bolt pouches can only hold 4 different kinds of bolts. To store bolts in a pouch, players have to use them with the pouch. Left-clicking on the pouch will open a menu showing players what bolts are currently in the pouch. Each of the four slots can hold up to 255 bolts. Bolts can be removed from the pouch or equipped by right-clicking on them. Mithril grapples, however, cannot be stored in pouches.
This item is particularly useful for God Wars Dungeon when doing Armadyl, as a majority of people use 3 types of bolts: Diamond bolts (e) & Ruby bolts (e) for the boss/minons and Emerald bolts (e) for killcount. It saves you an extra inventory slot for other items such as a Saradomin brew or Super restore.