Traveler's Backpack

The Traveler's Backpack is a 16 slot bag. It is similar to the Backpack that all newly created characters start off with. It ties with the Mooncloth Bag as the largest bag that does not bind (either when picked up or when used).

Source
This item is a World Drop from level 49-61 mobs, and also from mobs in Heroic Hellfire Ramparts.