The Flame in the Flood

In order to obtain this achievement you'll need to collect 4 pouches and use them to expand scout's backpack inventory.

Pouches can be crafted with a stitching kit + 2 rabbit hide.
Pouches can also be found as a very rare drop from loot-able areas.

Stitching Kits can be typically be found in medical areas or sometimes churches.
They can also be crafted with a fish hook + fishing line. Those two items are mainly found at bait shops. the bait shop icon looks like a building with a fish next to it.

rabbit Hides are obtained from killing and skinning a rabbit. 1 hide per rabbit. Create snare traps and put them directly over rabbit holes. If you've scared them all into their holes, just walk off the screen, and walk back and they should spawn again.
You can also kill them with arrows and a bow, but that's the least efficient way to do it especially when you're in the early game.