Tomb Raider (2013) - grind salvage points (MP solo) 

First (before salvage points and subject of this movie) we grind only medical supplies to buy characters and reach higher character level. 60 is maximum (very valuable "True Commitment" trophy/achievement).
Later do salvage points. Set one medical supplie like I in 'rescue' and grind salvage points (salvage points allow you to buy all additional upgrades and characters and reach also valuable "Shopaholic" trophy/achievement.