Are you going to be docked or at anchor while you eat, or will you be eating while under way?
Generally, finger food is better for boats than things requiring utensils. Also, I get seasick if I spend any time below, so I prefer things that are already assembled, or can be put together on deck.
Cooler space tends to be at a premium, and if there isn't enough ice, things might get a tad warm. So minimize the items that require refrigeration. And bring lots of beverages (especially non-alcoholic), because with this heat, you are apt to get dehydrated. Single-serve beverages generally work better than trying to deal with cups, etc.
Ginger helps settle the tummy, and is never a bad idea on a boat. Ginger beer, ginger snaps, ginger dressings....
As for specific ideas...none of these are earth shattering, but are simple and travel well.
* Grapes, apples, bananas, etc.
* rustic hard cheese, summer sausage and crackers or sourdough; consider slicing the cheese and sausage (and bread) at home;
* wraps: curry chicken salad; veggies & hummus; turkey, cranberry & brie; whatever sounds good
* cold fried chicken (I'd do boneless tenders or similar)
* cookies (bar cookies travel well)
If you are going to be anchored for lunch/cocktails, bring some fun dips and veggies, pretzel sticks, what have you.
Oh, and where possible, don't bring glass on the boat.