A flashlight (torchlight) comes in handy when exploring caves or when it’s night time.
It does rely on batteries so you’ll need to find adequate batteries as well. You can find batteries from caves and camp sites.
Here’s how you can find the flashlight (location) in The Forest.
Look for the cave entrance
The cave entrance is located in a wide area where the mountain is visibly at the back. You’ll also notice the river at the bottom.
The cave entrance is nearby, among the rocks.
The flashlight can be found at the exact location shown in the cave map below. It’s quite close to the entrance as well.
This flashlight is also in the same area where you find the katana.
The flashlight is in a dark hidden part of the area.