Ooh enjoy your upcoming trip!
I live in the Tropics so we go to the beach a lot!
I pack too much every time and figure, who cares haha! As long as I don't pay excess baggage I'm happy to have choices on what to wear.
I always bring a giant tote of some sort. (I'll attach a photo of my trusty LV neoprene monogram scuba). You need a giant open bag to dump towels in, sunblock, sun glasses, etc.
I bring my pochette for makeup and stuff and my key cles but those stay in the hotel room. I don't want salt water going near the vachetta!
I highly suggest a nice hat that goes with most of your outfits. I dislike hats but on the trips I forgo them, I end up borrowing my husband's baseball caps. Yucky in photos. So be prepared and bring a NICE hat that covers your face.
Bring sarongs if you have them. They are great cover ups after a dip in the ocean. And if you tie them around your neck, they can be halter top dresses. That way you can still walk to the room in style after a swim.
Bring conditioner for your hair! The ocean will make it feel like a broom.
Sunblock of course.
Ziplock bags to put your cellphone in while at the beach? (Sometimes the waves get rough and you may need this.. Or sometimes the wind blows the sand everywhere)..
Don't forget to pack going home clothes! I usually forget this and feel embarrassed arriving in the city looking like a half dressed beach bum!