One of the more useful NetHack tools. A Bag of Tricks is basically filled with monsters in fuzzball form. Taking one out ("apply"ing the bag) creates a random monster. A Bag of Tricks is generated with 1d20 charges. As long as charges remain, applying the bag has a 22/23 chance of creating a random monster and a 1/23 chance of creating 2d4 monsters.

When you try to #loot the bag for the first time, it will sprout a vicious set of teeth and bite down on your hand for 1d10 points of damage -- this of course identifies the bag (but it can be deadly at low levels, and this is an embarassing way to die). A Bag of Tricks can be recharged by a scroll of charging. When the bag is out of charges, it becomes completely useless until recharged.

Refers to a magical bag from which any number of wondrous things can be pulled. Felix the Cat was noted for carrying one. Can also refer to any package of handy or useful items or ideas.