A monopod should be adequate and would be a lot nicer to travel with than a tripod.

I would put a monopod in my checked bag for the trip. Could get by without it if necessary. But the rest of my camera gear ALWAYS gets carried on... no way I'd check it! Confirm the airlines size regs and be prepared to show that it's camera gear that's too delicate to be checked, in case they try to insist you do so.

A 150-600mm weighs around 4.5 lb. That might not sound like much, but added to camera, other lenses and accessories you can end up with a 25 lb. backpack pretty quickly. That's not heavy for short treks, but can be a real pain lugging through the TSA inspection and hauling around in an airport... or jogging to meet the connecting flight at the other end of the terminal! When I've traveled with a full frame camera I usually carry a 20mm, 24-70mm, 135mm and 300mm f/4 lens (~3 lb.), along with a high quality 1.4X teleconverter (which works very well on both the 135mm and 300mm lenses). Since then I've gotten an excellent 100-400mm (~3.5 lb.) that can replace both the 135mm and 300mm. It also works well with the 1.4X TC, if needed. Total weight is ~22 lb with flash, light meter, spare batteries, etc. in a LowePro backpack that fits in an airplane overhead compartment.

Heh Tugcapt...listen to what chg_canon says.
And, while you are allowed to bring cameras..that you can carry; a lens that big may have security asking questions and inspecting. Commercial photography is not permitted without a permit..and they may conclude that only a commercial photographer requires a lens that large. Also, no tripods are allowed. If you want to completely ruin your visit, then bring the lens. If crowded, they don't offer an extra seat in the 'welcome' theater presentation or on the launch for your equipment. And, they may not even allow you to take it on the Missouri as there is hardly room in places for you! Of course you can apologize to everyone bumping into you and your lens on the camera. I haven't even gotten to the sub.

OP said he was going to Maui and Oahu. I don't know about you; but everyone I know who has never been to Oahu wants to go to Pearl Harbor. And, anyone who has gone to take pics of the turtles..should find that the 300 reach is enough. And the OP does not sound like he wants to take all of his gear. Of course everything depends on where and what you are doing. And....I brought the 28-300 and 16-35 on my trip to Hawaii and could not have been happier. Most suggestions came from this site and a couple of pro friends.

Agree. I think you're much more likely to see turtles on the big island, especially on the Kona side. I don't recall seeing seals in Hawaii. Maybe I wasn't in the right place. Then again, I'm jaded as I live within a three hour drive of Monterey and Carmel in California where the sea lions hang out in droves. Sometimes they even come up the Sacramento River and can be heard barking in the Capitol city, 100 miles inland. Good luck getting those great shots.

If I recall correctly these shots were taken with my 18-200 Canon kit lens. But then, Monterey is not Oahu and these animals are used to people. I was able to get within about 10 feet of the sleepy guy. There was a stone wall between me and him. I would never approach one of them directly. The big ones have a mouth full of teeth like a bear and they're just about as big.

Sorry, don't mean to hijack the thread but I had to throw in my shot of the elephant seals that live further down the coast near San Simeon. I used my Tamron 150-600 on that one.