I looked at a couple side by side "coach guns" over the weekend that have me very intrigued. Short, but still with stock. I think it would double as a dandy canoe gun.
Personally, I keep and M1 Carbine in the truck. It rides just under the front seat on the hump. I figure it will be easier than pumping a shotgun, plus, either of my daughters can handle it. That is just what I am comfortable with.
I carry the same thing in my truck cab. I replaced the upper handguard with an Ultimak rail and mounted a red dot sight. I can even hit with it in the dark.
I think the shotgun may come up short against an assault rifle in a firefight, but depending on the range, and situation it is pretty difficult to argue with 12 gauge slugs or 00 buck. Most self defense shootings occur within 15' and you could be blind as a bat and still take out a combatant at that range. For what you want I believe a tactical shotgun can't be beat for affordability, potency, and versatility. Just my two cents.
I like the Kel-tec idea, and I always figured in a SHTF situation I'm going to take out the first goblin who accosts me and trade up to his weapons anyway.
Shotguns, generally speaking of course, do not make very good choices for open areas.
I was always told as a boy pistols and shotguns are good for just two things; Fighting to a rifle, and letting you get into something you should stay away from.
Buy some books and read up on E&E instead. With that mentality and two handguns you are more likely to get home, alive, to your long guns.
What one man go walk about gun fight do you plan to win?
For times when things are "hot" have a bag ready to go so you can carry long guns in and out of your vehicle daily. Neighbors see me with a lap top bag in one hand and gun case in the other.
For what you want a good choice is an 870 with 18" barrel, 2 shot extension and Knoxx folder. With a sling this gun carries very well. Compact when folded and stashes well. If you use Glocks A Kel Tec can be kept in a laptop bag with plenty of mags and ammo. It makes a good handout gun to a novice who may be with you while you carry the Glocks. Throw some mace in the bag too.