I use a Dakine hat. It does the job and is waterproof, reasonably comfortable too. There are others out there. Some use a plain old cap so it comes down to personal preference. I like the ones with a chin strap so it does not blow away. Some hats probably have zip pockets for keys wallett and phone, but do you really need it? I did hear of a guy whose hat blew off during a fast run. He turned downwind to retrieve it but failed to see the sandbank between him and the floating hat.

FCS do a good bucket hat with a stiff brim
if you prefer a cap, I got an Ocean and Earth mesh Truckers Surf cap, which has a strap. I've been happy with that too

I have a RipCurl bucket hat. It's much the same as the FCS, Indo, etc with a neoprene chin strap for stretchy comfort. I had to add a strap around the back of my head to stop it falling off whenever my head went under. A shoelace through the vent holes and over the top did the trick.

I liked and wore the FCS bucket hat for 4 seasons. I now wear the Garth helmet my wife bought me for Christmas.

A helmet that covers the ears and has a peak to shade the face. .

Add a neck shade tail where nessasary, but is generally less needed as the back of the neck is generally shaded a bit by the body leaning back.

Good point point Pacey. My ears are getting a bit munted, my cap's not the best for that. Might have to go back to the bucket hat. I removed the ear covers from my Gath as I didn't like the wind noise

After 30years of windsurfing and a squamous cell carcinoma cut off from top of my head few years ago,
I always wear a helmet now. Besides the sun, it also keeps me warm in winter and offers protection from the
occasional knock from the mast. Now that I've started foiling, it's essential.

I never seem to find a helmet to fit my very narrow, long head. I'm just too perfect aerodynamically .
Hats of all sorts tend to fly away in strong winds, so in light wind I wear an ordinary baseball cap and once it's blowing I swap it for a Gun Sails neoprene beanie, which has a cord to fix it to the wetsuit zipper. Generally it sits rather tight on a short crew cut, which I'm left with as the only possible option due to an extremely receding hairline . It tends to fly off in forward loop rotations, though. Hence the cord comes in handy.