These items help you improve your weapons or traverse the world. They’re usually found as you progress through the story.
Broadhead Climbing Arrows
With Climbing Arrows, Lara is able to shoot rough wooden sections of wall and rotten trees and then climb onto the Arrows. She can reach many platforms that weren’t accessible previously.
These are found as part of your progression, so they cannot be missed.
Upgrade Tools
There are three upgrade tools in the game. The first two are found in Strongboxes that are almost unmissable (you’re led directly to them as part of the story). The final tool is in the Supply Shack and can be purchased for a wealth of coins.
Upgrade tools give you access to weapon upgrades while you’re in camp. Selecting these costs a fair amount of crafting resources (Salvage, Hides, etc.), but they provide permanent bonuses to your weaponry.
Rope
Rope works with your Bow and allows Lara to break objects that have Rope Coils tied to them. She can finish many Rope-based puzzles, swing from hanging Coils, and generally have a good time creating her own zip lines between pairs of Coils.
You get the Rope as part of your story, and it cannot be missed.
Combat Knife
The Combat Knife allows you to cut down Flags, sever Ropes for a few puzzles, and to make special stealth attacks against unaware targets (which is part of an Achievement)!
The Combat Knife is found during the story, and it cannot be missed.
Rebreather
The Rebreather lets Lara swim underwater without the fear of dying. It’s a story item.
Suppressors
Suppressors dampen the noise of a weapon, making it harder for enemies to hear its report. It’s easier to make stealthy kills once you get these.
The Rifle Suppressor is a Mission reward. You get it at the end of Gulag Recon, in the Soviet Installation.
Oil Flask
The Oil Flask lets you collect Oil from puddles of Oil and from yellow Oil canisters. This material is essential for crafting homemade explosives of various sorts.
You get this as part of the story.
Weapon Sights
Sights improve the accuracy of your weaponry. They attach to your guns from a specific category (e.g. Rifles), and improve all of the weapons that they’re attached to. You won’t need to manually move the Sights around if you switch between SMGs, Assault Rifles, etc.
The Pistol Sight is a reward for finishing Dangerous Territory, a Mission in the Soviet Installation.
The Rifle Laser Sight is a Supply Shack purchase.
Grenade Launcher
This is what you get for the Rifle that already has everything. Once you grab this attachment, you can fire explosives out of your Rifle, dealing substantial damage to your targets. It’s effective against groups or for taking out individual enemies with heavier armor.
You purchase this accessory from the Supply Shack.
Wire Spool
The Wire Spool lets Lara grapple onto ledges, rockfaces, or hanging loops. She’ll be able to swing between certain gaps or pull herself to the top of the areas that she latches onto.
You get the Wire Spool as part of the story.