A bag is an item that can be equipped to increase the number of inventory slots you have. Each bag will give you an additional 25 slots, and each player can have a total of 3 bags: Your starting bag, which cannot be unequipped, as well as 2 addition bags that you can purchase and equip.
You can buy a bag at the tailor NPCs in any village, or at an NPC in your clan starter base. They are relatively inexpensive, costing only a few thousand gold.
The starting bag is not visible on the character's appearance. When equipping the first additional bag, it will appear as a backpack on the character. Further bags will not chance the appearance. A Deco will override the bag appearence.
A bag cannot be unequipped while there are still items in it.
Sometimes, a player's clothing may break due to durability loss. If this happens, the items in your pockets will be returned to your bag. If your bag is full, they go to a fourth temporary bag. You cannot add any items to that bag, and the bag is emptied and its contents are lost when the player logs out. Ideally, the player will make room in his normal bags and move his extra items there as soon as possible.
Bags with bonuses
In some screenshots from the Vietnamese and Korean versions of 9Dragons, there are pictures of bags that give various bonuses when equipped. It is not known how these bags are acquired or what the bonuses are.
With the release of Patch 63, a fourth bag is expected to be introduced to the game.