This trick requires a Sneak skill of at least 60. Go to Fort Independence with some scrap metal. Once there, speak with Protector Casdin. Tell him you have junk that you would like to give him. In return he will offer 5.56mm rounds, frag grenades, RadAways, and Stimpaks. Select whatever item desired, then save the game. You can then steal your scrap metal back from Protector Casdin. Sell the scrap metal back to him repeatedly to get as many of those items as desired.