Whenever you die before looting your stuffs from your former character that is now a zombie, your weapons and items will respawn in previously visited areas. If you scan the CCTV junction boxes, you can use the safehouse computer to investigate previously visited areas and see if the items have respawned there.
At Brick Lane Flats in the Old Brick Warehouses, there is a letter behind the door that requires a code to enter. For the code, step out of the room and look on the window to find an outline of the Raven Dee symbol on the glass. Line up that outline with the inside marking of the symbol on the wall with the cypher lock, then scan it with your tablet to get the code for the door.
When searching for the second book the doctor needs in the royal bunker, you will come across a door requiring a code that is obtained in the warehouse you go through. However, you cannot get the code until completing the Tower of London mission and receive the ability to read the Enochian language. Return to the warehouse and clear the area around the keypad, then enter the office beside the keypad room. Look through the glass towards the keypad and notice that the Raven of Dee above the keypad door is incomplete. Also there are some incomplete paint marks on the glass. Move around so that they line up, then scan it to obtain the code. Note: There are four digits spread out in the bunker. Besides the one in the mirror by the door, you can find others by following the trails revealed by your blacklight.