A Grumpy Greyhawk magic item - For all intents and purposes this seems to be a typical magical bag of holding, and even an identify spell will indicate this, although the caster of such a spell may get an 'odd feeling' about the item.
In fact, on the night of the next new moon, one object held within the bag will become possessed by a devil. If the DM must, a random roll is acceptable, but the devil does have a choice of which item he or she wishes to inhabit. Additionally, the devil can make use of what they've learned about the carrier of the sack from the time it was picked up 'til the time of possession.
The type of devil may, as well, be determined randomly, but will never be a unique sort, such as one of the princes or dukes.
Although the possessor has no inherent way of knowing this without some type of research, destruction of the sack will make the possession irretrievably permanent, but destruction of the item (no longer as simple a matter as destroying a mundane apple, extra shirt, ten foot pole or whatever the possessed item is) will release the fiend into the world.