This briefcase is located inside an old scrapped bus on the eastern side of Scrap Salvage. The bus is boarded up in the back, so use your machete to gain access.. You can find some ammunition right next to the briefcase.
Next to the antenna at the center of the region you can see a small makeshift car-shelter of sorts. On top of the roof you can find a diamond briefcase along with a water bottle; you'll find a ladder leading up to the roof right next to the antenna.
At the center of the Police Station you'll find a number of buildings. One of them has a diamond briefcase on the roof - you should be able to easily spot it from the ground. To get to it, you'll need to go to the building right next to it that has a number of wooden crates stacked up against one of the walls (see helper image in screenshot). Jump on these to gain access to the roof and jump from here onto the roof with the briefcase on it.
Just north of the Police Station you'll come upon a tree trunk that rests against a mass of rock (see small image). You can run up the trunk and drop down behind the rock where you'll find a diamond briefcase.
In the northern part of the region you'll find a bridge with a road going south on the western side. The road leads to a checkpoint; west of this checkpoint, next to the road, you'll see a small boarded up shack. Inside the shack you'll find the briefcase on the ground in a shallow hole amongst some animal bones.
At the northern part of the region you can find a checkpoint on the western side of the river. The building to the north of this checkpoint has a briefcase sitting on a ledge on the roof. To get to it, you'll need to jump up the wooden crates on the opposite side of the building.
The briefcase is located near the western side of the bridge at the northern border of the region. Beneath the railroad tracks there you'll notice a rock plateau. To reach it you'll have to follow the road west as it climbs up towards the tracks. Follow the tracks east and you can drop down to the plateau where you'll find the briefcase next to a body.
This briefcase can be found near the western rock wall surrounding Scrap Salvage. The briefcase sits inside an old train car that is half-buried in the ground. There is an old boarded-up bus right next to it, and you'll need to go through this to reach the briefcase.