I’m gonna have to go with an inflatable Kodiak.
They might have color TV by the time you get back.
Twenty two responses and no one has mentioned the obvious?
A life preserver. Everyone knows that when the boat is sinking the life preservers are out of reach–so you need to carry your own at all times!
An inflatable Kodiak? 
To each his own, I suppose; just remember to also pack some lube. And a repair kit.
Me, I’m bringing an inflatable boat.
I’d opt for a Zodiac.
- flare gun with extra flares
- satellite phone with solar powered charger
- mirror
- well stocked first aid kit
Ideally, a navy blazer with gold buttons. Ascot optional but preferred.
Bring a book on how to make a coconut nintendo system and how to train monkey butlers.
Before you go, be sure to check YouTube for instructions on how to build an exercise bike out of bamboo so you can power your wooden washing machine and various other appliances.
Oh, and bring your teddy bear.
There’s an awful lot of hysteria in this thread.
What could possibly go wrong? It’s just a three-hour tour. A three-hour tour.
Bring a credit card.
In case you see a boat you like.
I prefer sail boats.
I’d bring Jim Backus - he’s a hoot. And lots of big floppy hats for the sun.
Nitpick: The Professor never did anything with the radio. They did once manage to convert it into a transmitter… but that was the Skipper who did that. A convenient blow to the head managed to dislodge some of his Navy training that covered it. Of course, by the end of the episode, his mods got broken and he had another blow to the head that made him forget it.
Hey! At least the two of them are still alive!
OK — I’ll take Tina’s daughter, Caprice. But only because it will make you happy. 
…and maybe a pass for the LA Metro light rail system, just in case, well, things really go wrong. Like finding out the whole thing was just a dream, and you’ve really been on a Hollywood film lot all along. Of course, you could wake up in Kansas instead… nah… too improbable.
Probably you should bring along a good scriptwriter, as well. And your agent’s phone number on speed dial. And don’t forget the sunscreen, Kansas OR Hollywood OR tropical island, regardless.
A pterodactyl prone to saying: “It’s a living”.
Make sure you have the proper gear for dealing with Russian spies, mad scientists, broadway producers etc.
And kill the first mate before you even leave the dock.
Japanese/English dictionary for when you run across WW2 soldiers who don’t know the war ended.
Instructions on cannibal relations.
More Moxie. When Wrong Way Corrigan lands on your island, steal his freakin’ plane! Don’t just send him off and hope for the best.
Five years supply of transistor radio batteries.
Then you’d have a three hour series. Or less.
Remember the opening says the Minnow was saved by the crew, not just the Captain.