Bag of Exchange

This bag is simple in design, looking similarly to a Bag of Holding, except the design on the front looks like 2 bags parallel to each other, each one with an arm coming out of one bag and holding the opposite one, twisting in such a way that forms an infinity symbol. 

With this bag, you can put in one magic item, and the next day, you can pull a different magic item of the same rarity out of the bag. When one Bag of Exchange is placed into another Bag of Exchange, the Bag of Exchange will be turned into a magic item of a higher rarity. When a non magical item is placed into the bag, the bag will devour whatever item it was, including anything living. Any creature that starts its turn inside the bag is devoured, its body destroyed.

If the bag is pierced, ripped, or otherwise damaged, it will lose all magical properties, but before doing so it will create one magic item of a random rarity no higher than Rare (Common, Uncommon, and Rare).

This bag will only hold magic items, and the bag will grow in size in order to fit the size of whatever magic item is being placed into the bag. Afterwards, it will shrink back down to its normal size. The bag can also grow to release whatever magic item the previous one has been exchanged into. There is no way of knowing or influencing what magical item will come out of the bag. Broken or damaged magic items have no effect when placed in the bag, and will work like a non magical item being placed into the bag.

Notes: Utility, Container