long gun
When I was younger, it was not uncommon to see a deer rifle or shot gun, or .22 in the rifle rack of pickups. This was in Northern New York State! Now I live much further west, and it is still seen once in a while.
For anything I can think of that you might need to do as a private individual (not LEO), an AR would not be my choice for a truck gun. Too expensive if stolen, or taken by police, minor caliber, and scary to the soccer moms. A good ol boy Winchester or Marlin .30-30 (or better yet, a bigger cal) should handle the job nicely.
Lots of people today are hung up on firepower, whether they realize it or not. Just look at this thread, "should one carry an AR in your car?" Not a rifle, not a long gun, an AR15!
This is not meant as any kind of a flame, just an observation on where people focus.
For more than the last 30 years, entertainment media has shown us almost nothing but good guys and bad guys blasting the crap out of everything! And getting it wrong most of the time!
This seems to have had an effect on some of our thinking. Don't get me wrong, I like things with large mags, they are alot of fun, and we all should have some and know how to use them. It is our civic duty as milita members (unorganized). The example where a farmer used his .30-30 and ONE AIMED round to rescue the pinned down police officer is reasonable (even proper) but firefights are best left to the guys who get paid for it. It's not our job. I think a man with a nonparamilitary type rifle could hold out until help arrives.
I know that this is America, and many people think more is always better, so 20 or 30 on tap has got to be better than 5 or 6 or 7, right? Unless you are fighting off the dreaded mass zombie attack (who don't care about being shot), I can't come up with any situation where that much firepower is needed. If you make the first or second shot count (better yet first AND second) who is going to be stupid enough to keep on coming?
If an AR is what you have, and you want to keep it with you, go ahead, just remember, non-shooters see NOTHING but the abuse and misuse of tactical type firearms every time they turn on a TV, so be prepared for some people to freak out.