Fully upgrade a weapon.
You can upgrade weapons at Base Camps with the right amount of salvage and resources to improve damage, stability, ammo capacity, and more.
It may be ideal to focus upgrades on a weapon you use more than others. The bow might be the best choice here, if only because of how often you'll have to rely on it throughout the game. Otherwise, you may run low on resources quite often.
Once all the slots on a single weapon are filled, the trophy will pop.