It's nice but probably not necessary for most situations. I think the point is that, in most disaster scenarios, stores probably won't be able to take credit cards, and if you've traveled out of your local area, checks may not be accepted either. Seems like more and more people have less and less cash on hand. These same people will be in for a nasty surprise when the power goes out. <img src="/images/graemlins/frown.gif" alt="" />
In my experience, if you have more than $20, you're better prepared than the person who uses a debit card to pay for a $5 drive through order.