Story Related and Can't be Missed!
-Taken from the 360 guide, credit to ZidaneStrike-
*** Spoiler - click to reveal ***After you earn the "Headed Out" achievement, you will have a conversation in the woods with Uncle Pete and Nick. You can choose to be forgiving to Nick, but no matter which option you select, he will go off to hunt. He calls for his Uncle Pete shortly after and you encounter many bodies along the beach. As you are searching around, you will meet one of the scavengers that attacked Christa. He's pretty much incapacitated and he asks for some water. You can choose to give water to this man or let him suffer. Following that decision, two hordes will attack Uncle Pete and Nick. You will be prompted to save one of them. After making your choice, the game wraps up and you will earn the "Split Decision" achievement.
I personally chose to save Uncle Pete. I mean, at least that guy didn't fire a gun at me after I came to.
FUN FACT - The guy that wrote this episode is named Nick.