Imagine you had 72 hours before everything collapses. How would you spend that time? Would you stockpile supplies? Would you focus on warning as many people as possible? Would you try to preserve knowledge, like books, hard drives, download internet archives, etc.? Would you collect music or history?
The movie These Final Hours did a pretty good job of painting this picture.(spoiler: asteroid shockwave imminent)
And most comments here have covered the key plot ideas.