Rocket launcher. I actually know a guy who knows a guy who built his own once, but the FBI arrested him and he did a little time for that stunt.
I already have the butterfly knife, and a handgun, although I'm not sure what caliber the engineer's and scouts handguns are chambered for. Close enough. I don't personally own a shotgun, but my family in the other two houses on the property have all sorts of shotguns (crack barrel, pump action, automatic...), so that's also close enough for me.