The bag of devouring is one of the more interesting cursed magical items in Advanced Dungeons and Dragons (it also appears in normal Dungeons and Dragons). This item is one of the more creative ways to lose a character.
The bag appears to be a bag of holding, and will function that way for a time (a bag of holding is a magic bag that is larger on the inside than the outside). But it is really the mouth of an extra-dimensional creature. Over time it will eat the items placed inside of it. Its eventual goal is to eat its owner, which it will usually attempt to do after a couple of days. It usually waits until the person has his arm deep in the bag rummaging around for something (that the bag has undoubtably eaten). Then the bag will grab the person by the arm and attempt to pull them in.
Their is no way to recover someone that has been eaten by a bag of devouring. Although extremely powerful creatures may survive being eaten, ending up somewhere in one of the outer planes. The bag of devouring is very hard to destroy, as puncturing it causes the same deadly tear in reality, that ripping open a bag of holding does. There is simply no good way to dispose of one of these.