Each time a Survivor other than yourself is killed or sacrificed, Sole Survivor gains 1 Token, up to a maximum of 3 Tokens:

Each Token grants a stack-able radius of 20/22/24 metres within which the Killer is unable to read your Aura, up to a maximum of 60/66/72 metres.
Once you are the last Survivor standing, you benefit from the following effects:

Increases your Repair speed of Generators by +75 percent.
Increases your Opening speed of the Exit Gates and the Hatch by +50 percent.
Increases the odds of becoming the Killers initial Obsession by +100 percent.

The Killer can only be obsessed with Survivor at a time.

When another Survivor is picked up, Background Player activates for the next 10 seconds:

When you start running, break into a sprint at 150 percent of your normal Running Movement speed for 4 seconds.
Background Player causes the Exhausted Status Effect for 60/50/40 seconds.

Background Player cannot be used when Exhausted.

Reduces the volume of Grunts of Pain while in the Injured State by 25/50/75 percent.
Iron Will cannot be used when suffering from Exhaustion, but does not cause the Exhausted Status Effect.

Increases your Healing speed by 100 percent when healing a dying Survivor.
When performing any of the following actions, Were Gonna Live Forever gains 1 Token:

Performing a Safe Hook Rescue
Taking a Protection Hit for an injured Survivor.
Stunning or Blinding the Killer to rescue a carried Survivor
Consume 1 Token to grant the Endurance Status Effect for 6/8/10 seconds to any Survivor healed from the Dying State