If society collapses, just choose a usable frequency and a time to communicate with others beforehand, and probably it would be best to keep such transmissions short, should the TEOTWAWKI events take place. Not to protect yourself from authorities, who will undoubtedly be preoccupied with trying to hold together, but from potential marauders.
I doubt the military will be taking any measures against individuals using HF spectrum, they will have enough other problems to deal with aside from a few survivalists. CB would be handy in short range comms, as the equipment is portable, easy to use, and still plentiful.
And yeah, the spectrum is all 'spoken for', but in reality much of it is empty. The frequencies surrounding the CB band have been assigned to various governmental agencies for as long as I can remember and yet I have never in my life heard anything on those frequencies that remotely resembles a government agency transmission. Just outbanders.