To help out the community, I've decided to throw together a definitive guide to saving all the survivors in one playthrough. There are a total of 9 survivors, 11 if you include Dick, the owner of the pawn shop, and Jed, the psycho mechanic. Keep in mind that even though Jed the Mechanic and Dick show up under the Survivors list, they DO NOT count towards the achievement. Use whatever weapons you want, but i will make a couple suggestions for certain survivor(s). If you do this in order, you should unlock the achievement right after you rescue Bob and his daughter.
Before you begin, make sure you rescue Dick and get him to open up his pawn shop. Dick is on a van just outside the safe house exit. Keep in mind that survivors WILL NOT show up until you search the quarantine zone and bring the bike frame back. After rescuing Dave, you will not only have a source of quick and powerful weapons, but you will also have access to more Zombrex, which you are going to need if you want to nab this achievement. You only need two cases to complete this achievement and the game, but only one is required for the achievement alone. Be sure to buy a case of Zombrex from Dick if you plan on finishing the game. If not, just be ready to use the one you found in the ambulance. Also, be sure to visit Bob, who is on the roof near the Casino. He will be the one telling you where the survivors are. After visiting Bob, it's time to rescue your first survior, which happens to be the most lucrative group.
Gemeni and Fausto:
Gemini and Fausto are a couple found in the bar towards the north end of the map, but still very close to the gas station. Be sure to refer to the map. When you enter the bar, talk to Fausto. He will refuse to move until he has beer. Lucky for you, you're in a bar. Grab a beer from the counter and talk to him while holding it. Do that one more time. After he throws up, talk to him one more time and he is ready to go. Then talk to Gemini, who is right next to him. After a quick conversation, she is ready to go. Gemini is equipped with a big steel case of money, so she is able to fend for herself against a zombie that gets too close. That in no way means she can take on the horde. Keep a close eye on Fausto, as he is a druken idiot who can't fend very well for himself. He's also a bit slow, so don't rush ahead. Take the suggested route to the safe house and make sure both Fasuto and Gemini are standing behind you before entering the door and triggering the loading screen. If you don't you could wind up having to go in and out of the safe house two or three times, loading screens and all. After you get them both in, thats the end and you'll net yourself a very nice $15,000. If you come back to Gemini after you load out of the safe house and then come back, she will have another mission that can net you another $15,000. Two down, seven to go!
Archie and Jason:
Jason and Archie are a pair of guys who you would THINK can look out for themselves. They have what looks like BMX gear on, so maybe that would help them. Maybe the broadsword you have to give one of them to come with you would help. But believe it or not, these guys can get pretty out of hand if you aren't careful. Jason especially, in my experience. Be sure to check with Bob first, because this group doesn't show up right after you rescue Gemini and Fausto. You wouldn't want to waste time running all the way back there just to see that they haven't shown up yet. After Bob confirms it, DON'T GO RIGHT TO THEM. Instead, go to one of the two grey dots on the above map. The one closest to Bob is easiest, and you'll unlock the hunting store. Just go the roof and down the hatch to get in the Hunting Store. Alternatively, you can go along the awnings and head to the other grey dot. A broadsword will be waiting for you on top of the last awning. Either way, grab your new sword and bring it behind the General Store. Here you will find the pair fighting off the zombie horde. Give them a hand, then talk to Jason, who is holding the handlebars. He will tell you he wants a broadsword in exchange because the handlebars make a great weapon. (They don't) Equip the sword, then talk to him. After that, the two of them will follow you. Follow the suggested route, and keep a close eye on them. Even though one has a one-hit kill weapon, they can still get their asses kicked. Once you arrive at the safe house door, make sure the two of them are with you. Head on in, and drop off the handlebars while you are there. That's four down, five to go.
Nikki, Tia, and Shannon:
Next are Nikki, Tia, and Shannon. If you can call any of these survivor rescues a challenge, this is it. Your going to be severely handicapped throughout the mission, so stock up on good weapons, preferably firearms, and be ready to act fast. When you have your preferred loadout, which should include a case of Zombrex, head to Bob. He will tell you that he saw two girls walk into the bowling alley. Using the map, head on over to the bowling alley. There you will meet Nikki and Tia. They will refuse to leave unless their friend, Shannon, is with them. Shannon is in the quarantine zone, which makes this a difficult trek. After you talk to Nikki and Tia, i highly suggest building a paddle saw. If you need to know how to build one of those, refer to the collectible guide found on the forums. This weapon will be the best for thinning out the zombie hordes at the quarantine zone, making your trek back a bit easier. Equipped with your paddle saw, head to the quarantine zone. There will be heavy zombie presence in the area around the quarantine zone, which is where your paddle saw comes in. After you break the saw from over usage, head to the tent marked on the map and give Shannon the Zombrex. After that, she will join you. Do to her injuries, she is extremely slow moving. Walk up to her and press
to pick her up. You may be able to move faster now, but you can't use your weapons. This is why you can to clear out zombies before you got here. Run your way through the remaining zombies back to the bowling alley, and reunite the group. Now they will all follow you. You are still going to have to carry Shannon, but the other two are pretty slow as well. Unless your previous actions have left the main road less populated, follow the suggested route because there are less zombies in the back road. You'll have to put down Shannon from time to time and use those firearms i recommended to protect the other two, but with fast reactions and good aim, you'll make it back to the safe house in no time. Make sure the entire group is with you at the door, and then go in. Great job, it's almost over!
Bob and his daughter:
Ok, you're almost done and you are one survivor group away from your achievement. Lucky for you, the worst is behind you. Keep in mind that Bob won't mention his daughter being in the Hunting Store until AFTER 7:00PM, making this achievement a tight squeeze if you wanna finish the game too. I recommend grabbing some food before you go, because the falls here can cripple you against the zombies. After 7:00PM, head over to Bob and he will tell you that he saw his daughter head into the hunting shop. You can travel over to the hatch across the roofs like the first time, and you can walk in the front door if you unlocked it when helped Jason and Archie. Either way, get in there and talk to Bob's daughter. After a conversation, she will tell you that she won't go anywhere without Bob. Good for her, but now you get to walk back to Bob. Talk to him, and he will follow you back to the Hunting Store. After the couple reunites, (complete with annoying hug that blocks the doorway for a couple seconds) it's time to follow the suggested path to the safe house for the last time. Again, make sure they are both ready, and head in. After they thank you, BAM! achievement unlocked. Congratulations! You have just earned the Still Creek Savior achievement, netting you 20 gamerscore and the eternal gratitude of your new friends. So much work in such a short stay!
If i missed anything or anyone has any questions, feel free to post a reply here.