Matt 'Axe' Axelson: Are Mikey and Danny really dead?
Marcus Luttrell: I don't know.
Matt 'Axe' Axelson: Are we dead?
Marcus Luttrell: Not yet.
Matt 'Axe' Axelson: We're good right?
Marcus Luttrell: Fuck yeah. We're solid.
In the scene where Marcus is removing the shrapnel from his leg, when he gets to the last and largest piece, he places the medallion from his necklace in his mouth to bite down on. As the scene transitions from the leg to his face as it is removed, he appears to no longer have the medallion in his mouth. Then once the shrapnel is removed, he collapses and still has the medallion in his mouth.
The real Marcus Luttrell appears several times throughout the movie: he spills the coffee and tells the new guy to clean it up; he's in the operation briefing and shakes his head at the rules of engagement being read; and he's on board the Chinook helicopter when it is shot down.