In chapter 8, near the end of the mission, you will come to a shack with a power generator and some bunk beds.

There will be a random object in the middle of the shack, grab it, then leave the shack. The door needs to shut for this to work.

Then go back inside the shack and you'll see the item has respawned once more.

Pick it up, go back outside, come back inside, rinse and repeat.

Win!

You can use this to get as many resources as you want!