Glad to pass it along. I didn't discover it; I read about it on Scuba Board, then went out & discovered experientially that it's true.
Richard.
On those lycra socks:
Didn't have them during my first (and only so far

) LOB, in 2016 ... 2 successive weeks on the Egypt Agressor, which were great... Except my left above the heel area really might have benefitted from those socks... seems like either my boot or my fin strap tried to kill it. Thankfully I brought Gorilla tape... That was on that raw spot every dive of the second week.
So, duct tape, Gorilla tape is good to have.
I did not bring an extra mouth piece and my son and I both chewed through our first one. The spare one one of the DM's had was already chewed through... Found out only after already tiewrapping it on... Check first, duh... Good thing I brought 10 long enough tiewraps...
So the octo mouthpiece had to be put on the primary and the primary had to make do for a while on the octo... for me and my son... = 5 tiewraps used up in the action... Good thing I brought 10... left the others after the trip with the DM who could clearly need them...
So, a spare mouth piece per person and tiewraps would be good... Of course they should have been in my safe a dive kit, but I was at 50 dives then and had not thought I bite through that thing by 70 or such...
Had a whole bunch of stuff in that kit that was not needed. My rule of thumb: what's missing is what will be needed...
Camera: My camera gave up the ghost early in the second week. Died underwater, but died a dry death, the housing never leaked a drop, no condensation (brought plenty of little dried and sealed silkagel packets, a new one for every battery change). The camera just stopped working. Didn't think it would bother me that much , but it still bugs me. Can't afford these trips that often...
So, would a spare camera make sense?
In retrospect, yes.
I brought my Nautilus radio & an SMB and reel on every dive and made my son bring his SMB & reel. We carried whistles too. Not sure they would be that useful, but we had them on us. And we deployed one SMB on every ascend (unless it was by the mothership) for practise and to guard against zippy dinghies. A few times there was enough current and sea that it notably helped the dinghy in locating us - we were thanked for deploying it. Several passengers did not bring an SMB.
Imho definitely bring an SMB and reel per person... and what safety gear you feel you should have. I played it maybe a bit more safe because I would have not needed to return to my son's mother w/o him...
Motion sickness: I took the pills and needed them. My son was unphased by that.
Clothing: Did not bring much (I thought) and used only half of it nevertheless...
Gear and spare gear: Between my son and I we had a spare set of fins, spare straps, one spare mask, bungee cord, tiewraps, duct tape, first aid kit, o-rings, cordage, ..., some minimal tools to get at first and second stages and the hoses. needed none of it except tiewraps and duct tape. Schlepping (big, heavy) spare fins seemed stupid after the trip...
But, this summer my wife lost a fin in FL on one of her OW check out dives, the first dive of a 2 dive boat trip. No fitting fins on the entire big dive boat. Both checkout dives ruined... practically eight next to oodles of dive shops on Key Largo...
Now spare fins do not seem so stupid anymore...
I am not saying you should bring extra fins... my son and my fin size were / are compatible so it was only half the burden... just offering food for thought...
We had a few times waves high enough that loosing a fin when working up to that chopping boat ladder seemed like an achievable feat. Did not happen to us, but happened to another diver. Another divers fin (fulll foot) tore at the foot pocket. They were lucky to be helped with fins from the boat.
So anyway, think what should be in your save a dive / fix it kit as well as your first aid kit. Most of it may be available on the boat, ... except for when you need it...
Somebody already mentiobed a spare DC battery.
If your (dive) computer needs a charge cable, don't leave that right where you last topped off your computer before you headed to the airport... Did that for my first (and only so far) trip to Bonaire... duh... was a new, rare cable at the time too. Took a shop (after calling several) 4 days to get and I felt lucky they did. And they were unbeliavably kind just loaning it to me! ... Now, on an LOB ... in my case 2 weeks... that computer would have gone dead... One week, maybe it would have lasted... if I don't leave it in the rinse tank to long...
I brought tank marker lights for the night dives (as well as dive lights, spares, batteries, chargers), so I have a better chance to know where my son just went...
I know that should not happen, but trying to take pics at times makes you an awful buddy... I liked that tank marker light...
Whatever you do, test pack and weight your stuff with some time to spare... and maybe think again...