For a USA citizen in a non-commie state I'd recommend an AR15 (plus 22LR conversion bolt) and a 32 or 38 handgun for concealed carry. That will cover home defense, EDC and SHTF. You can branch out with hunting gear as needed.

In a commie USA state you definitely want a long gun for home defense if possible, which might mean something like a pump shotgun or lever action rifle. Your concealed carry will likely be a snubnose revolver. Alternately you might make/finish your own AR lower receiver and pistol frame.

In Europe you may be looking at something like a double-barrel shotgun for home defense but it will vary greatly by country.

Finally in totally non-permissive regimes you're looking at FGC9, zip guns, black market real guns etc.