Appetizer

Summer is my time to use wooden skewers. They provide endless options and you can get as creative as you'd like with fruit or vegetables, change them up with cheese and meat, add a leaf of basil, the combinations are endless. What I like best is you don't have to touch the food, just eat it off the stick.

Gazpacho is almost a salad in a glass. But cool and refreshing and peppery at the same time. Here's what I do https://food52.com/recipes/6047-allez-zpacho

I love this sweet/hot/salty melon salad by EmilyC: https://food52.com/recipes/12856-summer-melon-salad-with-harissa-feta-and-mint.

Really cold grapes in several colors & cubes of cheese

Smoked salmon on cucumber slices

"Beach dinner" makes me think "food on sticks"-- easy to prep ahead of time, pack, and eat. You could try a caprese skewer -- something like this looks good http://www.abeautifulmess.com/2013/07/peach-caprese-skewers-balsamic-vinegar.html -- or melon and prosciutto, like this recipe http://www.epicurious.com/recipes/food/views/brochettes-of-melon-prosciutto-and-fresh-mozzarella-108428

Pasta salad ( no mayo) vinaigrette with tomato red onion , basil and cubed mozzarella . Tabouli and or hummus / baba ganoush with pita chips. Crudité. Small cheese board,

Some thoughts jump to mind - do you want to balance nutrients (add some carbs), balance texture (add some crunch), ease of presentation (made & portioned in advance), means of heating or keeping food warm (or don't want to bother), go with what you're drinking.
So a few suggestions:
Spanish tortilla (potato omelet), served in cold wedges. as is, or with a sauce
poached seafood for dipping.
Smoked fish salad and good baguette
salumi on good breads or crackers
home-made seasoned nuts
home-made crispy seasoned garbanzos
old-fashioned but still lovely deviled eggs
Mexican street corn with cheese