Bag of Holding
A Bag of Holding is a magical sack that holds considerably more than it should; i.e., the space inside the bag is far larger than the size of the bag. Even the smallest Bag of Holding could hide an entire person, for example, though air is limited. As well as storing great amounts of things, the Bag never increases beyond a certain weight - so while a Bag may contain half a ton's worth of materials, the Bag itself will weigh a mere sixty pounds.
A danger of the Bag of Holding is that when the Bag is punctured, whether inside or out, all the contents inside are instantly destroyed.
One of these was given as the second place prize in the Great Carnival Contest.
Based on the D&D item of the same name, the full description can be found here: http://www.d20srd.org/srd/magicItems/wondrousItems.htm#bagofHolding