Use the right tool for the right job.
Your primary weapon may be a AR15, but you are not going to take it duck hunting in a SHTF situation and you need to put meat on the table.
Nor would you use that same over and under shotgun for duck hunting to fend off hordes of MZBs unless all other options have been expended.
If you can afford it, have a variety of firearms that best suit your particular location, situation and your actual expertise.