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?
To me, to even qualify as an apocalypse, it has to take out 99.9%+ of the population, and make extendedly staying alive stupidly difficult (and maybe even impossible) for anyone who “lucked into” surviving whatever it was that killed almost everyone else.
So it’s one of those things that is going to be hard to prep for with months and months of notice, let alone three measly days.