The guys have food, ammo and medical supplies. Sometimes they loot, but that's not enough to make a whole game (anyway, you could start 3 with a loot mission). But one time, a fire, earthquake or tornado (whatever) destroys their shelter. They have to search a new home.
Or, they find other survivors and have to rescue them. The rescued survivors tell them that millitary personnel built a save evac point and they travel there.
Or the village gets attacked by other survivors.
I have multiple more ideas, so PN me and I'll answer.
Greenies
have anyone told you this before?, mix your old shooter with the new "you choose your fate" games together.
im going to use DF: outbreak 2 game for an example EX: you walking down that hallway with the electrician and you need to fix the lights and electricity in the mall, here comes the choosing
" open door slowly and cautiosly"
"let him go first"
"kick the door open"
etc.
then the stroy goes on and yaddayaddayadda then zombies unseen from the shadows jump out, depending from the tools and weapons you scaveged, you can use those weapons to take down the zombies. and depending on how much medicine and ammunition you took, you will only have that much, and depending on how much zombies you have to fight off for each place (like the mall crew vs. zombies will have ALOT of zombies, way too many to finish off or that small room where there is only a few zombies) your chances of survival may vary from impossible to breezy. also depending of who your with (like a small group of people with weapons or an unarmed electrician) may either help you or slow you down or lower your chances of survival. it would be nice if you can use this type of format because alot of people is starting to miss shooting the zombies for themselves :P but people would still love to make their own choices. and you guys can manipulate these ideas into your liking with the other ideas for the third game. :) if you used this plz tell me :)