If I have a rifle, I never worry much about "back up". If you wound one and have to blood trail it, a handgun is sometimes easier to use in heavy brush, though. I'd take nothing short of a .41 magnum, myself. All those pop gun auto pistol calibers like 9mm and .45 ACP are worthless on a big boar except if you can make a head shot. If you have a 10mm, that would be the autoloader exception, and then with heavy loads.
A .308, a .30-30, a .243, a .45-70, a .30-06, IOW, a deer rifle is appropriate for hogs. Use a little tougher bullet on the big stuff. I like Barnes or Nolser Partitions. Shotguns are for dove hunting.
You could use a slug, but I don't mess with slug guns. Rifles are far more effective hunting arms. If I'm going to limit myself by choice, I'll take my Contender pistol in .30-30 or my .45 Colt.
Hogs ain't man killers and they ain't THAT hard to kill. Just like bear, I hear all sorts of legends about big hogs. Main thing is, use a good bullet, one that penetrates, and put it on the shoulder or head, not behind the shoulder. There is nothing, but guts behind the shoulder. Hogs can be dangerous, especially wounded, but they're not man eaters. I know a guy that got ripped from his belly button to his right nipple, but he was stabbin' a 350 lb hog with a knife at the time. IOW, he was askin' for it. I've been out with guys with hog dogs before, kinda nuts if you ask me. They can't get at ya if you're in a 10 foot tripod stand.