John's Treasure Box

 is an ammo box in the North West part of the Scrapyard, in a burnt out bus near a red container (see location image on this page). It contains:
 * Grognak the Barbarian
 * U.S. Army: 30 Handy Flamethrower Recipes
 * Guns and Bullets

It can be unlocked using John's Key, which is on a random encounter: Wastelander being attacked by three dogs. The Wastelander will also have a note describing where to find the box. The Wastelander is usually dead by the time the player reaches him, although it is possible to save him.

Videos
Fallout 3 Guide: John's Treasure Box Location