Wear a Big Hat
You need to keep the sun off not only your face but your ears and the back of your neck. If you prefer a baseball cap, put plenty of sunscreen on your ears. And, just for today, turn the bill to the front.
One dive boat rule is that anything fragile ends up under somebody's weight belt. Leave your Oakleys at home and take cheap sunglasses instead. All sunglasses sold in the U.S., even the cheap ones, must have some ultraviolet protection, and most meet the ANSI General Purpose standard: 60 percent UVA protection, 95 percent UVB. Polarizing cuts glare.
Break the Wind
Protection against wind, not to mention spray, is critical to staying warm on the way out to the dive site as well as on the way home. A windbreaker, even a raincoat, will help, but a dive parka is better. Wind and waterproof, a dive parka is lined with fleece, which keeps you warm even if damp. It has a hood, and it's long enough to protect your legs if you sit on a wet bench.
Use Death-Grip Clothespins
If you drop your pants in a puddle, you want to hang them up somewhere in the sun and wind. But use industrial-strength clips and clamps, not those wimpy wooden things Mom used in the backyard. One-inch carpenter's clamps are one possibility. They can grip thick parkas and sweats and have a very powerful spring. You'll find them at the hardware store.
Take A Dry Bag
That means a real dry bag, not a lined pocket in your gear bag or a "waterproof" bag with a conventional zipper; the zipper will leak. This is a personal-effects bag, separate from your scuba gear bag. Put everything inside it that you want to still be dry after your last dive: your shore clothes, your wallet and a big towel, for example. Try not to put things in it you'll need sooner so you don't have to open it often. You can keep it out at your gear station with confidence that the inside will stay dry no matter what.
Take an Extra Towel
Take a second small towel for wiping your face, your exposure suit, your camera and your first stage between dives, saving a dry towel for later. Pack it in your gear bag, not your dry bag. Chamois-type camp towels work well.
Wear Deck Shoes
Your Nikes are going to get wet and trashed. For a cheap and, if necessary, disposable alternative, go to the discount store. Eight bucks can buy a pair of canvas slip-on shoes with deck-gripping herringbone soles at Kmart. Wear them with polypro or wool socks to keep your feet warm when they get wet.