In your carry on you need what you can’t borrow IF your checked bag doesn’t arrive with you. Being Cayman that’s your bathing suit and maybe your favorite tee wrapped around your camera, dive computer and reg. Your primary mask that you know won’t leak unlike rentals that may or not fit.
Don’t put your c-card in the checked bag, without it the above is useless!
Yes bring the BC he is used too! And if you are close on weight, take the cam band off and wear it as a jacket :)