All of the various types of collectible items are described here with no spoilers. I have also created separate quick guides to all major collectibles, which should help if you miss anything during your own explorations but don't want to bother with the full walkthrough.
Equipment – Consists of objects Lara uses to interact with and get around in her environment, such as the torch she acquires in the first level and the axe she finds a bit later on. You must obtain each of these in the game before you can use it. Because the equipment list contains some spoilers, it can be found on the separate Upgrades page.
Weapons and Weapon Parts – There are four weapon types in the game: bow, pistol, rifle and shotgun. You begin with no weapons at all and gradually acquire weak versions of each type, which you can then improve as you advance through the game. Some weapon upgrades are achieved by finding a better version of the same weapon, some by spending salvage points, others by finding weapon parts and combining them. Weapon parts are usually found in salvage containers but may also be obtained by looting dead enemies or raiding certain Challenge Tombs. (See the Skill, Gear and Weapon Upgrades page for a detailed list of weapon parts and their locations.)
Ammunition – Ammunition, presumably left behind by the island's inhabitants, can be found scattered around most areas. At first these are just bundles of arrows, but later you'll find boxes of ammo for other weapons. Searching the bodies of slain enemies will often yield ammo as well. To pick up an item or loot a body, stand near it and press Interact. These screenshots show the different ammo types.
Food Caches and Edible Plants – In addition to hunting prey for food, Lara will encounter a few other sources of food on the island. Food caches are small, orange boxes or coolers that yield Experience Points when opened. Some areas also contain edible plants that can be picked for a small number of XP. (screenshots)
Salvage – Here and there you'll find small, wooden crates and larger chests or trunks containing salvage. Stand close to a crate and press Interact to pry it open with your axe. To open one of the larger trunks, stand close and tap Interact repeatedly to pry it open. (screenshots) I guess the contents represent random junk that Lara can use to fix and upgrade her gear, but in gameplay terms you get salvage points, shown by a counter at the top right corner of the screen. (screenshot) Gradually these points add up. When you visit a Base Camp, you can spend points to upgrade your gear in various ways.
There are other sources of salvage besides crates and trunks. Hanging nets full of salvage must be burned in order to free the crates inside. In the early areas, you can use your torch to do this. Later on you'll have to find creative ways to reach high hanging nets. Looting the corpses of fallen enemies may also yield salvage. Raiding each Challenge Tomb gives 250 salvage points. So these "optional" tombs are definitely worth the effort.
Unlocking certain skills will enable you to collect more salvage from containers and/or the animals and enemies you kill.
Skill, Gear and Weapon Upgrades are covered in detail on a separate page.
Documents – Others have visited this island before Lara. They've left traces behind, including various notes, letters, diaries, etc. As you find and read them, more about the island's history and inhabitants is revealed. You also gain XP each time you find a document and bonus XP for finding all documents in a particular set. To re-read a document, go to the Map screen. Then navigate to the Documents screen and select the one you want to examine. (See the level walkthroughs and the Quick Guide to All Documents for details.)
The location of each document found is also marked on your map screen. The map key shows how many documents are hidden in the current area and how many you've found so far.
Lara's Journal Entries, which she makes periodically while resting at base camps throughout the adventure, describe events from her perspective. You can review them on the Documents screen as well. They do not count toward the total number of documents in each area, though, since they may be unlocked at slightly different points for each player. The last one is unlocked when you beat the game. (See the level walkthroughs and the Quick Guide to All Documents for details.)
Relics – These are interesting and sometimes valuable objects left behind by past inhabitants. You also earn XP each time you add a relic to your collection and bonus XP for collecting complete sets. Relics you've found are noted on the map screen, and there's a separate Relic screen so you can peruse your collection. Each has a unique appearance and provenance so be sure to examine them carefully. (See the level walkthroughs and the Quick Guide to All Relics for details.)
GPS Caches – These are little containers hidden in hard-to-reach places. Using Survival Instinct will reveal them, but even then, they can be hard to find. GPS caches yield XP when found, and you get an extra XP award for finding all caches in an area. Like documents and relics, GPS caches you've discovered are noted on your map. The map key also shows how many caches are hidden in the current area. (See the level walkthroughs and the Quick Guide to All GPS Caches for details.)
Treasure Maps – In each area where there are no Challenge Tombs, but there are Documents, Relics and GPS Caches, there is a hidden treasure map. When you locate this map, your in-game Map screen is updated with the locations of all of these items. The ones you have not yet collected are shown with a question mark (?). Items that are inaccessible because you are missing some necessary equipment are shown with a padlock icon. Unfortunately the treasure maps are usually harder to find than the treasures they reveal, but you do need them for 100% completion.
Raiding each Challenge Tomb also provides a partial treasure map, showing the locations of relics and documents or GPS caches only. (See the level walkthroughs and the Quick Guide to All Treasure Maps for details.)
Challenges – In addition to the collectibles listed above, many areas also include optional challenges, in which you must locate a series of objects and do something like shoot them, set them on fire, etc. These are separate from the Challenge Tombs. The number of items you must find is indicated in the map key for each area, but the items themselves are not shown on the map, even after you find them. They are marked on the annotated maps linked to each of my walkthroughs. (See the Quick Guide to All Challenges for details.)
Again, check the walkthrough for help finding every collectible item in the game. Or, if you just need help finding one or two key items, refer to the Quick Guides to Documents, Relics, GPS Caches, Treasure Maps, and Challenges.
†UPDATE HISTORY: 8/13/13 - Page first posted online.
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