If you have a sneak rating of at least 60, you can attempt this infinite goods trick, which takes place at Fort Independence. Head to Fort Independence with a bunch of Scrap Metal in your inventory. Once there, speak with Protector Casdin and tell him you've got junk you'd like to give him. In return, he'll offer up 5.56mm Rounds, Frag Grenades, RadAways, and Stimpaks, and you can choose which you want. Then, save your game (in case you fail the following) and steal your Scrap Metal back from the Protector. Sell the Scrap Metal back to him over and over again, thereby netting you infinite amounts of 5.56mm ammunition, Frag Grenades, RadAways and Stimpaks.