I can provide you with some suggestions to get started:
Title: The Last Hope
Act I:
The play opens with a monologue by a survivor of the world war, reflecting on the destruction of planet Earth and the loss of countless lives.
The survivor encounters a group of other survivors who are struggling to come to terms with the aftermath of the war and the harsh realities of their new existence.
The group decides to embark on a mission to find any signs of life or hope for their future.
Act II:
The group travels through a desolate and dangerous landscape, facing various challenges and obstacles along the way.
They come across a group of people who have established a new society, but are facing their own challenges and conflicts.
The two groups must work together to overcome their differences and find a way to rebuild and sustain their new world.
Act III:
The two groups face new threats and challenges, including a lack of resources, environmental hazards, and tensions between different factions.
They must find a way to come together and make difficult decisions to ensure their survival and the survival of their new world.
The play ends with a hopeful message about the resilience and determination of humanity in the face of adversity.
This is just a starting point, and you can make any changes or additions to the story as you see fit. Writing a play is a creative and challenging process, but it can also be a rewarding and fulfilling experience.