I gotta tell ya', draw that line pretty darned close to "essentials". Your personal space will be roughly six feet long by two feet wide by two feet high...your bunk. Inside your curtained bunk space you will have a small reading light and hopefully a "hammock" style net on the wall. While it's true that most of your diving/camera gear will be outside on the gear deck and you can keep extra dive gear there, your space out there is restricted to what can fit under your seat. (tank, BC, regs are left connected for the duration of the trip. Your wetsuit will be hanging up on bars on the central part of the gear area.) My advice is take only what you absolutely MUST have. I might carry a spare mask and maybe maybe another reg, but that's about it. Pare it down to the basics if you can. That bunk area is awfully tiny.
By the way...keep doing those weather dances.
From the NWS for the Gulf of Mexico, 110 miles out
"SAT
W OF FRONT WINDS INCREASING TO 20 TO 25 KT. SEAS BUILDING
TO 4 TO 7 FT. E OF FRONT S TO SW WINDS 10 TO 15 KT. SEAS 3 TO 4
FT."
Not looking too promising, pardna', but keep the faith. It's marginal, but not truly discouraging...yet.
Have fun!