To easily get items, you will need a Sneak skill of 60 or higher. Go to Fort Independence with some scrap metal and speak to Protector Casdin. Tell him that you have junk(scrap metal) that you want to give to him. He will then offer you 5.56mm rounds, Stimpaks, RadAways, and frag grenades. Save the game. Steal the scrap metal back from Protector Casdin and then sell it back to him again to repeat the process.