I got this on my way to the Gateway to the Hills. I chose "backroads" and had to stop in Sedalia for supplies. There are 3 optional Survivors in Sedalia;
Jimmy Blake at the gas station - Wants you to find his Uncle's Keys to generator so he can trade you gas for a ride.
Warren Bedford, who is on the roof of the Food store (1st bldg you enter). He wants batteries for his radio, which you will find on the 2nd floor of the police station (the room that is at the front of the bldg on right side--if you were viewing from street), and;
Deputy Kessler, who is in a prison cell of his own volition with a stash. He will trade you some supplies for food.
You have to work your way through food store on left side of street so you can't miss Jimmy Blake (he calls you to roof and asks for batteries). He says he'll cover you from there, but don't believe him--he never fires a single shot). He'll also tell you to go find Warren Bedford in the gas station (which is on the right side of street directly across form police station. To get to Warren, go back in the door closet to the ladder down from roof and go out front door. Warren will then send you to the trailer park to find his Uncle. The trailer park is behind the Police station. After getting key and return to Warren, as soon as you press "x" to talk to him the achievement will pop. You can start the generator and fill your gas cans and leave or also give batteries to Blake and food to Kessler.
In the end, if you help more than 1 survivor, you can also get You Go Your Way, I'll Go Mine - Dismiss a Survivor, since you don't have enough room for more than 1 additional survivor and you have to dismiss others.