Hero's Sack

The Hero's Sack is a national treasure of the former Elfrieden Kingdom and Kingdom of Freidonia. It previously belonged to the first King of Elfrieden. In RPG-type games, this would be referred to as the Item Box.

Description
The Hero's Sack is basically a plain-looking, squalid bag that resembles a sandbag used for boxing.

Abilities
The Hero's Sack is a bag that is able to carry far more than its outside volume. It is also able to keep items in a kind of stasis. Food items are kept from spoiling, and time seems to stop within its confines. Poncho Panacotta was able to keep foodstuffs in the sack for over two weeks.

The maximum volume within the sack is unknown, as well as the limit of items one can carry. For all intents and purposes, it may have unlimited storage space. What's even more surprising is that the added mass of the items is negated when carried in the sack. Genia Maxwell had actually submersed the bag  in a river for half a day, and despite having more than 80 cubic meters of water, debris and fish inside of it; she could still carry the bag with ease.