Good point! You know, back in the day when they used to hunt black bear up in the smokeys with dogs (before the feds stepped in and made it park), a lot of the bear were killed with .22 rifles after they were treed by the dogs. Many a man has been killed by the lowly .22 as well. A good .22 does have it's place.
A brick of .22 doesn't weight a whole lot either, maybe 4 or 5 pounds. What's 500 rounds of .223 or 7.62x39 weight? 20 or 30 pounds?
I think a Ruger 10/22 with Taurus .22 revolver (9 shot) or a 10 shot automatic pistol (pick your favorite brand) could be a viable combination, though I'd probably carry something a bit bigger for a primary pistol.
One thing I've always thought about in a SHTF situation is that I'm not going to be looking to primarily fight my way out. That would really be the last thing I'd want to do. I'd want to sneak around. If your sneaking, your chances of living are a bit better than if your fighting. I'm not sure a 500 yard rifle is a necessity. If I'm that far away, especially in East Tennessee, I might as well be a 100 miles away.