For best ending you have to survive till phase 3 I did it by staying with Bob
Going to the market when his leg was fractured
Offering bob to go with the helicopter
Wandering about and reaching the trapdoor to meet Olive
when he runs out of food supplies go to the girl in east and take her secret stash
Offering to get infected and then injected
Go to complex of stores nearby
Offer the man a cure
Lie to the three axe men
Run away with the cure to military base
This is based on my memory doesnt cover each and every step