Here's a listing of what I used to stay (nearly) sunburn free while fishing for a week just a couple hundred miles off the equator. As usual, these are affiliate links. Your purchases help support moosefish. Additionally, Deuter provided a pack because I'm an ambassador.
Since you can't always be covered start with a layer of sunscreen. I used Banana Boat Sport SPF 50. It's waterproof, broad spectrum, and not stinky. Super bonus: It's cheap at just a couple of bucks for an 8oz bottle.
In spite of all the jokes, wearing a pair of running tights kept my legs from burning. Darker colors are more likely to scare fish, so a pair like these gray Nike Mens Pro Hypercool Tights would be better than the black pairs I had. If you're going to be in the water every day be sure to bring two pairs so you can rinse each night and let dry the next day. Bonus: You can sing, "We're men! Manly men! We're men in tights!" Correction: You are required to sing it.
(Not needed for sun protection, but for modesty: Columbia Sportswear Men's Silver Ridge Cargo Shorts. These are my usual hiking shorts, too.)
Up top I used two different types of shirt. The first was a long-sleeved cooling shirt from Huk. It was super comfy in the heat. The only problem was without a collar it exposed the back of my neck and I got a bit of a burn there. (Yes. In spite of the sunscreen.)
The other shirt I wore was a Columbia Silver Ridge long sleeve shirt. It doesn't cool with magic (like the Huk), but with the collar I didn't get burned on the back of my neck. I did, however, get sunburned when I neglected to button it up all the way on the first day. Pro-tip: Button it up all the way.
On my feet I wore a Simms Neoprene wading sock that prevented damage from stray coral that snuck in my boots. And speaking of boots...
I started with an older pair of quality wading boots that were well past their expected lifespan. They lasted almost through day four, but gave it up as we were finishing the day. The only other footwear I had with me that would work were my Keen Newport H2 sandals. This wasn't the first time my Keens have saved a trip. In 2015 I found myself at the trailhead without boots and climbed Red Mountain in the Alpine Lakes Wilderness in my Keens. And just like that time I wore socks with my sandals. The only problem this time was they were wet when I got back to the lodge.
Even with all that there was still skin showing and clearly that won't do. So...
Add a Huk Fishing Next Level I.C.E Gaitor. I wore the gaitor pulled up over the top of the head to protect my neck, ears, and nose. Pro-tip: Wear it the right way around and it won't feel so tight and will let your breath pass through a little easier.
For a hat I had an Outdoor Research Active Ice Cap. It was super light, has a "split brim" so you can fold it up, and a cape to cover your neck or that you can tuck up underneath if you're an adherent of Edna Mode. Best of all is an elastic cord you can pull tight so it doesn't blow off when you're on the boat zipping between flats.
Also from OR: Active Ice Sun Sleeves and Active Ice Spectrum Sun Gloves. The sleeves pull up to mid-bicep and have both a thumb hole and a slot for your middle finger. The gloves extended about an inch up my wrist and fit perfectly. Both are UPF 50+ and legitimately cool when they get wet.
The final, and perhaps the most important piece of sun protection are sunglasses. Pretty much everyone agrees that they must be polarized and should be amber. It's also good for the glasses to block light from the sides, but that doesn't mean they need to be full on glacier glasses. I wore my Smith Outlier Carbonic Polarized Sunglasses. The polarization cuts the glare and sort of lets you see through the water. I like the amber lenses because they both reduce the light and enhance the color. The only downside is most of my pictures don't look as good as what I was seeing. (And just in case they fell off my head I had Chums to hold them in place.
Beyond sun protection, there was some other critical gear for a tropical fishing trip. I primarily used a Sage four-piece, eight weight rod. Sage rods have never let me down and a four piece is so much easier to carry on a plane. I am still using an old Lamson reel, but the line is a newer Scientific Anglers Sonar Saltwater line. Most others had straight up floating lines, but mine was an intermediate line so it sank a touch. There were certainly times when I was hitting the fish and others weren't so consider a slight sink on your lines.
I carried everything, including snacks and water (in a Source Hydration Reservoir) in a Deuter Compact EXP 12 pack. (Special thanks to my Deuter friends for shipping me the pack on short notice.) The Compact EXP is technically a bike pack, but it worked perfectly for fishing the flats.
I was on the flats under either completely or mostly sunny skies for about nine hours a day for six days straight. While others were burned I came back to the Northwest roughly the same color as when I left. Don't get me wrong, I've had plenty of sun failures on the sun and above tree line, but at least this one time the right gear saved me.