Plan for as much room as you feel comfortable with taking up in your living space. This question I assume implies a shelter-in-place (bugging in) scenario. Remember, water is the essence of life. One cubic foot of storage space per person for each two days is a starting point for planning for water. One cubic foot of water is about 7 gallons IIRC. You may want to go higher. Play around with various foods to see how much storage space a day/week/month's worth takes up.
If the disaster is a tornado, which is likely, then I really can't prepare for it unless I have enough baskets to distribute my eggs. If it is a tornado, then there wouldn't be a store nearby to reopen.
Jeanette Isabelle