Prepper Stash: Pooper Scooper
Begin this even-more-disgusting-than-the-name-might-indicate prepper stash at the Silver Lake Summer Camp, southwest of Drubman Marina.
Look for the large building toward the southwest end of camp. There will likely be one hostile here, banging on the door.
Off him, then turn around and read the prepper note right in front of the camp message board.
Enter the large building from the west. There's a scaffold you can jump up to, and slat-battened window you can smash through.
Inside: tons of dogs in various states of distress, and tons of poop.
Interact with the poop to search it. You'll find all sorts of things, including live ammo and a wolverine skin, but eventually you'll find the deposit with the key. Use the key to unlock the door.
The key will open all the other cabins, but the stash is in Cabin 2.
Enter the stash to complete the mission. The other two cabins have a wolverine and a mountain of dog food, respectively, but no noteworthy loot.