Suffice it to say, that you must hoard small portions of cash, and it's better to spread it around than to keep it all in one place (e.g., not just under your mattress).
You'll also need to be extremely frugal during the first 72 hours with your cash. Try to work out deals, barter, or otherwise create on-the-fly IOUs. Short of creative financial deals, you'll need cash.
How much? Well, it's up to each person to determine that. But assuming you've got several days' supplies of food, water, and shelter, you won't need much. I can't really see more than $100. You may even be able to get by on $20.
Where to store the cash? Remember, as in anything financial,
Store small bits of cash in your house. Store some outside. Put some in your car. It wouldn't be a bad idea to put some in a safe deposit bank at a couple banks in town.
Remember, you're not trying to store wads of cash; keep in mind that you may "lose" this cash, so don't go crazy and put your mortgage in a cookie jar.
There are many novel places to store cash in your house. Let your creativity guide you.