Prepper Stash: Playing with Fire
Look for this stash at the Hope County Jail Bus, west of Fall's End in John's region.
It's usually guarded by a trio of cultist campers.
Dispense with them (this is a good place to practice your pistol takedowns), and search the bus for the prepper note.
Follow your marker to a nearby sewage tunnel. There's a right (west) branch here that will lead to the stash, but ignore it for the moment, and go straight through to the other side.
There, in addition to an angry bear, you can find a guy who was just mauled by an angry bear, and a key.
Grab the key and re-enter the tunnel. Now you can follow that branch, though watch out for a wall-crawling wolverine that may be resting here.
Enter the stash to complete the mission. Note that this not only gives you access to the usual loot, it also makes your molotov crafting more effective.