I wear a baseball style kook hat with chin strap. I wear sunnies with strap. A couple of times a session I get worked by the waves and the hat flips back and off my head. Getting it back on is a pain with the sunnies etc, and often I have to go in to sort it out. What do others do? The chin strap is about as tight as I can go without it becoming uncomfortable.

I have the same setup but not the same problem. Hat flips off but stays wrapped around my neck, sunnies (seaspecs) stay in place due to a fairly tight strap. Hat then takes 1 second to pull back onto my head...

Are you putting your sunnies & strap on over the top of your hat strap? If so that will be your problem

I go with any trucker/baseball style cap. I put a bungee under the chin and expect it to get pushed backwards every time I hit water. The bungee just catches around your neck and it's not hard to quickly slide it back in position, even over sunglasses.

There's two reasons why your hat gets flipped off backwards. The obvious one is that you're hitting hard and the brim is catching water and flipping backwards.

The other is the hat is badly designed. The straps on the side have to form a wide based triangle a bit like the straps on a clubbies cap. The straps have to join the edge of the hat near your temples and almost to the back of your head. If the strap is close to your ear it will just flip off.

Some hats have soft brims that flex, but it's the configuration of the straps that make the biggest difference.

I added a strap to an old baseball cap. It never comes off. It's the similar to the clubbie ones below but without the bow. The chin strap just slides under my chin. The rear straps are set a little further back than in the pictures and slide freely on the chin strap. You slide them up, put the chin strap on, slide the other down and away you go. The ribbon can be put up inside the hat if you want to wear it out of the water.

I have a really old Dakine cap that is perfect. It has a long stiff brim, wide triangle ear covers and it never comes off. It refuses to wear out but the fabric is all bagged out. The new ones look ok but a bit flimsy. FCS do decent hats too. Patagonia are garbage.

I wear a bucket hat, it has a really floppy brim. It will only fall backwards when I have a huge crash. Also then get sun protection on your ears

Wear a helmet......