Thus by picking up a quest item and starting the DLC before finishing the quest relevant to the item, the player character may "smuggle" equipment into the Sierra Madre. However, anything flagged as a quest item cannot be removed from the inventory in addition to having no effect on WG.
Another way to do this is to activate a Stealth Boy and walk (not crouch) straight up the stairs opposite of where Father Elijah walks down. The charges should go off and kill Elijah and one will complete the quest and be able to escape with over a minute to spare along with all the loot in the vault. One will phase through and fall but will get back up on the opposite side of the door near the exit. He will then open the shield (make sure one is walking into the door). Destroy one or two of his turrets (having Christine on still alive will help). Co-operate with him then run (walk) out of the vault with everything and press up against the shield door where the charges are placed. Then they must grab everything in the vault and then talk to Elijah from the holographic projector. The player character must have an abundance of C-4, gas bombs, or demolition charges and place them in front of the shield door where Elijah confronts the player character in the vault.