Tom-
It was an excellent trip! The Virgin Islands, especially St. Johns (STJ), are insanely beautiful. I recommend that anyone looking for a short trip to paradise, this is the place: it's a short flight from the US, and you don't need a passport. You can hike the National Park on STJ (and camp, if you want!), lounge on a beach, snorkel, scuba dive, and of course, do all sorts of photography 
We stayed on St. Thomas (STT) because the wedding we were attending was held there; in the future, I'm going to St. Johns straight away. The best beaches are there, and also smaller crowds compared to the more built up St. Thomas. Reason being is that cruise ships regularly dock on STT and dump 3000 people, so it gets crowded. It costs $20 for a round trip ferry ticket from STT to STJ, and then cab fares ($16-$18 one way), so it adds up if you figure out too late that STJ is where it's at (like we did).
General tips:
- Sun screen, lots of it.
- Bug spray: the mosquitos weren't a factor while we were there, but they are reportedly bad, especially if it has been raining. You will also run into biting No See-ums, especially on the beach after the sun goes down. There's a reason why every front desk/hostess booth has cans of Deep Woods Off available for public use.
- Food is expensive. $25-$35 per meal, and that's not including drinks (if that's your thing). Because it's an island, prices are higher. If you stay in an Air B&B, I highly recommend hitting up a food store the first day there, and stock up.
- Cabs are expensive. Rent a car if you can, but beware: driving there is scary. Lots of hairpin turns, blind corners, and the roads are super narrow.
- There's a guided bird walk, hosted by the US Park Service, at 7:30 AM Friday mornings at Francis Bay on St. Johns. I didn't make it to this because getting there from St. Thomas was a hike, but next time I am most definitely going.
- On STJ, there's a bar right off of the Redhook ferry in Cruz Bay called Joe's Rum Hut. Try the Lime in da Cocount drink, it's delicious.
- Bring snorkel gear, you can jump in pretty much anywhere. Trunk and Cinnamon Bay were excellent.
Now to the stuff we all want to read about 
Photography gear, or "what should I take??".
5D4: awesome, didn't miss a beat. For wide angle stuff, you want a FF sensor. If you are primarily birding/wildlife, go with an APSC. Because I was using the 16-35, the FF camera had to come along.
16-35 f/4: was great for all around use, though some may prefer a 24-xxx variant. You can't go wrong with either. I'm not much of a wide shooter, so it was a nice change of pace for me working with the wider FOV.
50L: was the least used, simply because this is a bright, outdoors sort of place, so the big aperture is not needed, and you generally are wanting wide or telephoto. The only place I used the 50 was at the wedding we attended. If I am going to an urban area, the 50mm would see a lot more use, but for future sunny trips I'll probably leave this one back home.
100-400 II: most used lens, by far. I won't lie, this was a heavy beast to lug around, but because I mostly shoot birds these days it was a sacrifice I was willing to make. I came away with some photos I truly love. Used it with the 1.4x TC 99% of the time. If I wasn't shooting birds, this lens would be hugely unnecessary.
What about a macro lens? I normally bring the 100L with me on travel, but this time I took to 100-400. For Caribbean islands, I'd skip the macro because there are just about ZERO bugs. There are a good amount of flowers though, so a macro lens might be better for your needs. When I go to Costa Rica someday, the macro will definitely be in the bag.
Tripod: didn't use it. IS on the 16-35 f/4 did everything I needed.
430EX flash: didn't use it.
ThinkTank TurnStyle 20: excellent bag for walking around. Hold just enough gear, and it's comfortable.
ThinkTank Airport Essentials: insanely good bag for travel, though I think I'd rather get a more hiking backpack style for future trips.
If I were to do it all over again? Tough call because bird photography is my interest these days, but if I were to re-wicker my bag for general purpose travel (to USVI, or anywhere), it would look like this:
5D4 (or 6D, depending on if you are ounce counting)
16-35 f/4: this lens is awesome. 16mm is perfect for city/urban trips, but outdoor stuff I think I'd rather bring a standard zoom
OR
24-70 f/4: small, sharp, macro mode if necessary
70-300L: smaller than the 100-400, great zoom range
No primes. Thin DOF stuff just isn't my thing anymore, and if it is dark enough where I have to shoot at f/1.4 I should probably be on a tripod anyway, which I wouldn't be bringing either.
A small Fuji kit would be nice too, but I've yet to branch into another system.
Birds: there are a number of birds on the USVI that we don't regularly see stateside (at least where I live in MD), so I thoroughly enjoyed chasing down what the islands had to offer. You regularly see Bananquits, Pearly-eyed Thrasers, Green-throated Carib hummingbirds, and a good number of doves and pigeons. There were more obscure species that I didn't happen upon (Mangrove Cuckoos, numerous shore birds, Antillean Crested hummingbird), so I need to go back at some point and complete the scavenger hunt
BeachesI mentioned beaches... Needless to say, almost all of them are world-class. White powder sand, turquoise blue waters, the quintessential idea of paradise.
This is Trunk Bay, regarded as the best beach in the USVI.
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I actually preferred Cinnamon Bay because it was more quiet, and there were a number of Brown Pelicans there. No, I didn't get any photos of them this time... but now I have a reason to go back
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That's all I have for now, hope I didn't bore you with the trip details
