In the beginning when you are outside of the warehouse in the rain, there are two vans in front of you. One of the vans will be locked. Open either the side or back doors of the other van to get Painkillers and a 9mm pistol.
In the warehouse after the cleaning imposter tries to trick you, kill his teammate. In the room his teammate came out of is a forklift with a board and two barrels. One is an explosive. Push the lever on the forklift and the board will slide backwards, allowing you to walk up it. Then, jump to the box. Turn around, then jump to the other box. Jump to the box next to it with a open box to find grenades, painkillers, and ammunition.