Friendships, you can call them and ask them to activate special perks to help you out of a tough spot, as indicated below.
If you sufficiently improve your relationship with certain other characters in the game (i.e. Tier 2 Weapons (Bat, Grenades, MP5, Carbine) Tier 1 Weapons (Knife, Molotov, Uzi, AK-47)
Many of these cheat codes will prevent specific achievements / trophies from unlocking, so make sure you save your game before entering cheats.
