With all of our knowledge and science, there's literally no good reason why anyone should ever not have enough to survive. We just suck at getting it distributed equally and fairly because of greed.
How about, and I know this is a mind blowing concept, but rather than trying to pick who lives and who dies, and prepping for a world where lots and lots of people die, we build a world where we don't HAVE to pick who lives and who dies.
Because everyone lives.
Yes, even the people you don't like and who don't like you.
When you start from the position that allowing large amounts of people to die is considered an "acceptable loss", you've ALREADY lost. You've shifted everyone into the scarcity mindset of "I gotta stab everyone else in the back to make sure I get mine".
You START the problem solving process with the fundamental that each and every person lives. That they all have shelter, food, water, medicine. You don't even get to begin to discuss who gets a second helping until everyone has had a first helping.