In it Lara stores her Inventory. Her weapons, her infinite ammo, the artefacts and keys she collects, spare clothes, the medipacks... everything she can carry away.
This small canvas knapsack has leather straps and is used to carry all of Lara's inventory. She found the backpack during her travels with Von Croy at the age of 16. While exploring in Angkor Wat she discovered it in a hidden chamber, along with the skeleton of its unfortunate previous owner. She has carried it with her on her travels ever since and is very rarely seen without it.
The backpack in Tomb Raider Legend has changed considerably. It is no longer able to hold unlimited items. Lara can carry only one additional weapon, 3 medical packs and whatever relics she finds in her journeys.