I see that you need something casual and cute, functional yet chichi. It has to survive the fishing but pass at the dinner.
My recommendation? Go with denim capris, something washed but not too beat up. Preferably with cuffs. Then some real leather sandals with an open toe to show off your nails and a kitten heel. You'll look gorgeous when yopu meet him, and they're easy to take off for the fishing. Plus, the bottoms of your capris should be high enough to not to get all wet and saggy. On top? Something airy but cute--one of those peasant blouses maybe, in white or yellow or something like that. It is spring, after all.
If you don't have a bathing suit yet I recommend something colorful but tasteful in its coverage of your nether bits. WHATEVER YOU DO, STAY AWAY FROM A THONG. You will look like a lady of ill repute when you sit down at dinner and everyone spots the dreaded Y peeping over the top of your good-girl capris. Stay away, I say.