The fact that no one knows what it is we are trying to survive from is the reason to own and shoot several types of firearms.
If I were bugging out for some reason I would certainly want a hand gun. I own a .45 but I would probably ideally have something that holds more and lighter ammo, like a 9mm. Depending on the circumstances it might also be handy to have an AR-15 or even a shotgun with you as well.
If I were attempting to stay in my home but needed to protect it from invaders for some reason then an AR-15 would be invaluable but having a number of weapons scattered throughout the home along with plenty of ammo would be the key.
For the purpose of only occasional protection but mostly food providing, I would choose a 20 gauge shotgun but I would also want a .22 rifle available to shoot small animals at long distances and because ammo is small, light and cheap so you could easily stockpile thousands of rounds.