Soul bag

A soul bag (often referred to as a shard bag) is a bag used by Warlocks to hold more Soul Shards than they would normally be able to carry in conventional containers.

The soul bag consumes a regular container slot, however, so it reduces the number of available slots for non-Soul Shard items. The value of the trade-off is up to the individual Warlock.

Soul Shards harvested by the Warlock are automatically stored in an equipped soul bag when acquired, making tedious Soul Shard housekeeping a thing of the past.

Helpfully, soul bags also display the number of soul shards stored within them on the bag icon on the container toolbar.

Cataclysm
With the soul shard system completely revamped, the soul bags were no longer needed. Most of the bags can no longer be acquired, while existing soul bags were converted to smaller normal bags.

Types and how to get them
Soul Pouch - 20 Shards
 * Pattern sold by in Gadgetzan for.
 * Tailoring skill needed: 260

Core Felcloth Bag - 28 Shards
 * Pattern drops in Molten Core.
 * Tailoring skill needed: 300

Ebon Shadowbag - 28 Shards
 * Pattern sold by Andrion Darkspinner in Shattrath City for.
 * Tailoring skill needed: 375

Abyssal Bag - 32 Shards
 * Pattern sold by Duchess Mynx and requires reputation with Knights of the Ebon Blade
 * Tailoring skill needed: 435

Removed soul bags
Small Soul Pouch - 12 Shards
 * Rewarded with the ability to summon the Succubus.

Box of Souls - 16 Shards
 * Reward from Strahad Farsan after doing The Binding quest, along with the ability to summon the Felhunter.

Felcloth Bag - 24 Shards
 * From book that spawns after you kill Jandice Barov in Scholomance.
 * Tailoring skill needed: 285