A small guide with the locations of all the lost items present in the game (obviously it can contain very small spoilers).
Locations of All Lost Items
In the beginning of the game (just before exit the building and receive the walkie-talkie call) turn left into a locker room, the lost item is inside one of the lockers.
As soon as you use the key to open the locked door, you will see two bathrooms, open men’s bathroom door to find the lost item inside.
In this part of the map there are a lot of stairs, the lost item is on a high pipe, to reach it, just climb a vertical tube that is on it’s right.
No Way Out
In the office, the Lost item is right next to a computer.
As soon as you enter the sewers you will see a 3D printer, take the path to the left to find the lost item.
Before going up the ladder to get out of the sewers, turn left into a room with a 3D printer and the lost item.
After a while in the city you finally find the house you need to get in, go downstairs to the basement and you will find a chest with the lost item inside.