Unlock: Finish the “Kick the Hornet’s Nest” story mission.
The “mystery man” who gives you the quest also gives you a scanner. It pings more rapidly when you’re getting closer to one of the packages he’s lost. To finish this quest, he needs you to find and photograph the barcodes on those five packages, which are liberally strewn across the nearby jungle.
You can comfortably expect a lot of encounters with animals while you’re tracking the packages, such as bears, snakes, and a crocodile that’s waiting in the river. The scanner’s pinging tends to drown out animal sounds like snakes hissing at you, so stay on your guard or bring a few Hunter’s Instinct syringes.
The first package is at the base of a cliff and is easy to find; the second’s stuck in the fork of a tree. To get to the third, you have to stand on dry land somewhere near the shipping crate in the river and shoot the chain off its door, then swim over to it. There are a couple of crabs in the shipping crate, and if you haven’t already found one on a beach somewhere, you can kill a crab to unlock its entry in your Handbook.
The fourth is out in plain sight near a fork in the river, while the fifth is on a ledge behind the nearby waterfall.
To photograph the fifth barcode, you have to get down to the water from the cliffside above, then climb up some vines on the east side of the river, deal with a snake, jump across a gap, then carefully move across the cliffside to get to the ledge with the barcode.
Weirdly, simply photographing the last barcode is enough to finish this mission. You don’t have to return to the mystery man.