I am very blessed to have Dale as my dive buddy. He is great in the water and makes my diving so easy and seamless. He checks and double-checks all the dive gear packed and our in-water time is perfect.  

However, topside is always my department. He does not check or double check what I bring. But while on board the boat he will ask me if I brought this or that and I usually forget something. I was always forgetting many of the same things. Well, I finally started taking an inventory and will share some suggestions. Some may not work for all and at my age I think I have started bringing more than I ever have, but it is still a rather small list that still fits in my backpack.
For seasickness prevention I do not go anywhere near the water without Bonine™ as it works best for me. It was a trial and error process that made for some miserable trips when other products did not work. Find what works best and stick to it.
Along with Bonine, I bring a small supply of Tylenol and antacids. Visine makes a great line of “summer” products that work great for sun and sand and saltwater for my eyes. I keep one of the small bottles in my dry bag.
I have a terrible time sleeping away from home. I will not blame it on the bunks and engine noise as it happens anywhere I am away from my own bed. Sleep aids help, but on a dive boat and knowing I will be diving in the morning and need to be awake and alert, I usually refrain from “sleep-aid.” I have found that natural sleep aids work best for me on dive boats. There are several on the market and you can try them at home first to see if they will work for you later on a boat. Remember, you don’t want to be drowsy or impaired in any way. I tried a new sleep formula called Zazen that is all natural and helped me to sleep, though I had a difficult time getting passed the taste. There is an over-the-counter natural hormone called meletonin that I have found to help me sleep with no grogginess in the morning. As with any product, you should try it first and maybe check with your doctor if you worry about interactions with any medications.
I always make sure I have my driver’s license, c-card, DAN card, credit card, Bonine, Tylenol, antacid, sunglasses, Visine, hairbrush and sleep aid. I hate to admit this, but now that I am a lot older than when we started California Diving News, I now carry a small medicine case to put my old lady prescription meds in. 
Dale brings his computer on most trips, which really makes me nervous. I will only bring my iPhone or iPod. Pelican Products has made a great protective case specially made for the iPhone or iPod. It is the i1015 case and fits the iPhone, iPhone 4 and iPod touch, though a variety of other smart phones will fit inside the case.
What makes this case wonderful on dive boats is that it keeps my phone dry, yet I have full access to my music through a waterproof external jack that I plug my earphones in. While they tell you not to fully submerge the case, it is the same quality construction that Pelican is known for. I do have waterproof headphones that I use in conjunction with the case to listen to while damp, wearing my wetsuit in-between dives. No more worries leaving the phone on the table and wondering if wet divers will drip on my cargo. Check out Pelican at www.pelican.com.
Another nice product I use is a small dry bag. IST makes and excellent small dry bag (www.istsports.com). Some dive boats don’t have room in the galley for every single diver to leave a backpack to keep things in reach. I do know most deck hands will tell you to leave everything below deck and they will get it for you. But I don’t like to have to tell them to search in the backpack and bring me my Tylenol or any other personal items. I found my small dry bag is great to keep a handful of personal items within reach. If there is room in the galley, I can tuck it away there. If there is no room in the galley it fits in my dive bag on deck and stays dry. 
One last note on keeping things dry –accidents happen. Things get moist or even wet no matter how hard you try.  There are post accident remedies out there.  One of note is the “Bheestie.” It is a pouch filled with moisture removing beads that can be used after the accident happened. Of course with electronics there are no magic cures or guarantees, but this may help and I have seen it work. The Bheestie is also recommended for maintenance of those electronics that may be used near moisture. Tuck your phone or other electronic in the back for a few hours to suck moisture away before it does damage. Check out www.bhessetie.com for further info on the bag.