You can't beat a 12 guage shotgun for stopping power. I'm not impressed with the 5.56 (223 cal) as a defensive round...I would buy a 7.62 (308). I own a Mossberg 500 12 guage shotgun for defense. I also have a Winchester 30-06 and a Ruger mini 14. Both of my daughters and my wife have 38 or 357 revolvers and I have a 45 Glock.
I have a M1903A3 for distant targets 600-800 yards, the M-1 for closer in, and the 12ga for personal distances. Backup is the Ruger .45acp.
BTW all, MAKE SURE that you have sufficient amounts of food, water, and something to COOK WITH! Several bags of charcoal and a hobo stove does the trick. Also, make sure that you have a gallon of plain bleach for water purification.