Due to modern conveniences and the 24/7 culture "we" have become complacent and reliant on short-term food supplies. The average grocery store only carries a 3 day supply and must be constantly replenished. The average family (non-preppers) only keep approximately 3 days worth of food on hand.
Therefore, in the event of a SHTF event, society is 3 days (9 meals) away from anarchy. People will panic when their limited food runs out and there's nothing at the grocery store and no money to make purchases.