Salvage

Salvage is essentially a form of currency in the Survivor Timeline of Tomb Raider.

Tomb Raider
It is usaully in the form of small yellow wooden boxes, but salvage can also be found when looting dead enemies/animals, looting Hidden Tombs, and in large grey metal containers that must be payed open. Salvage is used to upgrade Gear in single player.

Salvage points can be spent on upgrades, which improve various aspects of Lara Croft's gear. Along with skills and its associated Skill Points, Gear form the upgrade system of the game.Each gear upgrade requires a certain amount of Salvage be spent on it.

Parts
In addition to salvage, the player may find weapon parts for a particular weapon (except the Axe, which is upgraded only through the story). With enough parts (2 for the Recurve Bow, 3 for others), the weapon will be upgraded to a more advanced model, and more upgrades will be unlocked. Previously purchased upgrades will carry over.