Never “field dressed” them. Bring home alive if possible and place in fresh water bath for a week to purge.
Otherwise shoot them between the eyes with .22, push clothes hanger type wire through the hole wrapping it around lower and upper jaw. Snapper can bite several hours after death. Scald in boiling water, hang by wire, cut off all claws and use filet knife to “unzip” along the hard top shell and lower soft shell. Remove guts and filet the meat out of the hard shell. Use the filet knife to remove the skin as you would filet a fish.
Muscle tissue will continue moving a lot during this process. If you have not lost your appetite yet: soak meat in mild salt water solution overnight, drain and pat dry.
Season to taste, roll in flour & or corn meal and fry. Also makes good vegetable based soup.
A snappers has 7 distinctly different flavored meats – enjoy.

It is easier but more barbaric just to use a tomahawk to get to the meat. In a survival situation, you can get inside the shell if you can, cutting out the offal. Just throw on the coals to cook.