The good news is that you need very little. If you came to Flores with a small bag, just bring it all on the boat. Otherwise, make a daypack with just a few things for your tour and store the rest at your hotel.
Bring: snorkel gear (you can rent it), camera (underwater), sunscreen, bathing suit, money, easy hangout clothes (sundress, shorts, tanks), rugged flip flops, toothbrush, hairbrush, phone/camera charger.
Optional:, sweat towel, rashguard, something to cover from the sun, insect repellent (just in case), a book or something to do for hours.
Living on the BoatThe covered deck is basically your living space so your luggage lives on the deck next to the beanbags and sleeping mats in "your" spot. This is where you sleep, hang out, and change your clothes. You're on you own to figure out where to put your stuff including your wet clothes and snorkel gear.
There's only one small wet toilet on the boat for changing your clothes so count on changing your clothes surfer-style on the deck. There is a fresh water spigot in the toilet, but don't plan on showering.
Unless you paid for a private cabin, you will be sleeping on the deck with everyone else and will just crash out in whatever you're wearing. A sheet and a real pillow are provided. It was comfortable but a bit chilly. I was glad for the flannel sheet. If you get very cold, you might wear something warmer or bring an extra sheet.
There are electrical outlets throughout the boat for charging your devices.
What You Need for the TourThere are usually a few hours in between sights so you are hanging out on the boat a lot reading, napping, taking in the scenery, or face buried in your cell phone.
The only things you need money for are park entry fees (Rp 470,000 total), crappy souvenirs on Komodo island, large Bintang beers for sale by clever entrepreneurs who paddle up in their boats (Rp 50,000), and possibly snorkel gear rental before you board the boat (Rp 50,000). That's it.
I didn't see any mosquitoes my entire trip so I didn't need any mosquito repellent.
Tour StopsFor visiting the parks, you can get buy with rubber flip flops but they're not ideal for the hike up Padar since they get so slippery from sweat. But for Rinca and Komodo, they'd be fine. I suggest a rugged flip flop or better for the entire tour. I would have been 100% fine if I had only brought my Reef Fannings.
Our first day was Rinca Island, Komodo Island, and Pink Beach so we were in walking clothes most of the day. Rinca was hot but mostly shaded. Komodo is all flat, nothing rugged.
For hiking to the view point at Padar, it doesn't matter what you wear other than maybe some sun protection. I just threw a sundress over my swimsuit. Padar is mostly stairs (some wood, then rock, then dirt and rock) and at the tree it turns to more of a regular trail.
Our guide went in bare feet (!) and I went in rubber flip flops and wished I had my Fannings. It's hot hot hot. Bring a sweat towel. No matter what shape you are in, you'll be dripping with sweat and have that extra glow for your postcard perfect photos at the top with the view.
More Details About the TourBooking a Komodo National Park Tour - What You Need to Know
What to Bring on Your Komodo Nat'l Park Tour
Visiting Komodo Dragons in Indonesia
Pink Beach, and Pinker Beaches
Padar - THE Komodo View Point
Manta Rays - Majestic Giants in Komodo