What ever the divers who came on the boat brought. I eat what ever looks good while they are down on there dive.
In all seriousness I tend to raid my cabinet of dive food every morning before a day of diving. Drink wise PowerAids, or Gatorade. Food wise cheese crackers, fruits, a good grinder, my daughters little gold fish bags, fruit cups, pudding cups, cheese sticks. My spouse says she has to feed two children every day.
Avoid anything with a strong aftertaste. Brownies, Cookies, etc. I worked at a shop that would serve little brownie bites between dives and I hated it cause for the next hour all i could taste was brownie in my reg. And of course when you see them all the boat you can't help but eat them.
I know its extremely non-AWARE of me but often I will eat sushi on dive boats. Its light on the tummy, no after taste, theres often ginger in it which helps with sea sickness (if your prone to it).
DO NOT EAT THE CREWS / CAPTAINS / INSTRUCTORS FOOD! Im not kidding customers eat my lunch all the time! "It was in the cooler, I thought it was free"