A thinking prepper is going to have a modern pump air rifle because you’ll never run out of rocks/ammo to shoot for either self-defense or wild game. These can also be purchased pre-crisis without arousing the tracking/ire of Big Brother.
Moreover, the closer to a city that you get, the more valuable stealth defense items become such as soft body armor panels.
Likewise, in many cases it may be that your best defense is simply to remain locked up out of sight while others outside take each other out. For this option you need food/water already stored. Also, your local climate may dictate that you need solar power or heat/fans.
A pistol and long gun that share the same ammo also makes sense, e.g. 22LR.
On the wild side, you can buy 3 watt infrared lasers now that can blind any opponents even in large numbers. Some people are home-building 10 watt lasers. Remember to wear your own eye-protection, especially if you begin to see newly blinded survivors roaming around you.
Speaking of which, FLIR has gone up in quality and down in price. Useful at night.
I’ve read, somewhere, about old Mexican guys that had black powder shotguns. For shot, they’d pick up the larger pieces of silica grit that ants had brought up when building their nests.
I am a huge fan of air guns! Can’t imagine not having them. So useful, for no signature and cheap ammo. A lifetime ammo supply for just a few bucks.