Crossbows...at least high powered ones are actually pretty loud. My wife has an excalubur 440 Assassin that is as loud as a 38splSilent but deadly.
I stated in the posting that you should, "consider the problems and events of the day" for your answer. What you think you need is entirely up to you. The intent was to think about what calibers might available if it all went south. It's all well and good to have the latest and greatest, but can you get ammo or components in the worst of times. Lugging around 150 rds of 308 and 120 rds of pistol adds up real fast. I've done it, but it hurts. Days gone by. I hope.The answer depends a lot on whether you are remaining in a static location or bugging out. Guns and ammo are heavy especially if you are carrying othet supplies (food, water, med kit, etc). Ive carried a firearm professionally in some of the most inhospitable places on earth....it is not easy. A PWS Mk216 (308) with 6-25rd pmags of 308 plus a 65# ruck sack will wear you out in short order. This is one of those times where a handgun/rifle of the same caliber would be VERY handy. Whether its a 9mm Semi Auto/carbine or a levergun/revolver combo (my preferance). However, remaining in a static location presents a whole different set of problems.
Longest standoff the better, so whatever can reach out and touch those that don't matter. With 8 in the family I have my own pack mules and probably just as stubborn! All will have a sidearm, 2 shotguns, 4 intermediate rifles and 2 long range guns. Just shy of a squad.