May I suggest
Listening to Katrina and gleaning some information from the site which can be found as a Sticky in Strategy & Tactics?
http://www.thehighroad.org/showthread.php?t=356667
My experiences and observation with serious situations, concurs with the author of LTK, in having a sidearm on person.
Personally, I would add a second gun just like it, so ammo and if a semi-auto, the mags will work for both.
Now what I and mine have done, and more than once , and includes making a run to Katrina to give guns to our folks that lost guns, were Model 10s with standard pressure 158 gr LSWC and LRN.
During Tornadoes, we used Kel-Tec P-11s with standard pressure 115 gr JHP and FMJ, and standard pressure 124 gr JHP.
Youth single shot 20 ga shotguns were also employed.
Here is the deal based on my experiences, and I am going back to when I was a kid in the 50's.
Matters get serious, and concealing, being mobile with, being in control of the firearm, and the simple user friendly aspect is important.
By "controlling the firearm" I mean being in direct control of its whereabouts, and it not being lost or stolen.
Sidearms are easy to keep on person, that youth single shot is not but 36" long, and it too is easy to keep up with and even conceal.
Broken down, it really is easy to tote and have control of.
Anyone from a kid, teenager, adult, elderly to physically limited can use these guns.
Simple manual of arms, and these "fit" folks.
Single shot shotgun is simple to use, and is also more "friendly" in various jurisdictions, in regard to "guns" and "gun politics".
One has to sleep, so a teenager, elderly, physically limited person can keep watch with one of these platforms while you sleep.
If one gets hurt, again, others may have to use the platforms you have.
Again, go visit
Listening to Katrina, the gun goes on person, concealed.
Other more important physical items are discussed, as are pre-planning and preperations.
Not every situation is best dealt with, with a firearm.