Usually, during times of severe weather forecastings, I get inquiries about what I have in place to prepare. Here are my suggestions, but, as I have always encouraged, do your own research:
#1 ASSUMPTION: Focus on the assumption that ALL public utilities (water, sewage, electric) will be unavailable or contaminated and that you will not be able leave your house for a week or more. Calculate your needs based on what, and how much, you use on a regular basis then add to that by 10% just in case things get worse or friends/family need assistance.
#2 ASSUMPTION: I understand this may be contrary to those "glass is half full" thinkers but this will help prepare like your life depends on it, and it may. Assume things will get much worse than you can possibly imagine. Imagine every possible scenario and prepare accordingly.