On the western side of Sepoko, right next to the northern observation post, you can find a small shelter with metal sheets for a roof. On the roof you can find a briefcase. To reach it, climb the observation post and jump from there onto the shelter.
West of Sepoko - directly south of the safehouse in the north-east - you can find a large tree next to some cliffs. There's a fire here as well, making the area easy to find. Right next to the tree sits a briefcase along with some ammunition.
In the south-western part of the region, close to a checkpoint, you can find a small body of water surrounded by large rocks. On the north-western side you'll notice a fireplace; right next to it lies a briefcase.
Up on a cliff here sits a briefcase on a crate; there's a water bottle and some explosives nearby. You cannot reach it by foot; instead you'll have to use the Hang glider located to the south-east of this place.