This is my guide for a tropical vacation in Okinawa. I went in February, when the weather bounced between 10deg to 25deg, so keep that in mind.

What to take on full day outings

• Backpack about 15L in volume. You can carry everything listed below, plus lots of items you may want to bring home with you
• Tylenol, preferrable the daytime type because it does not contain an anti-histamine (chlorpheniramine maleate) which can make you drowsy.
• Allergy medication, desloratadine works well for me.
• Kleenex
• Lotion
• Sunscreen
• Passport, requested when checking into hotels.
• Lip balm
• Hand soap
• Extra pair of socks
• Bus/train fare
• Headphones
• Auxiliary phone battery
• USB-A to USB-C cable
• Wallet
• Phone
• Keys
• Hat
• Sunglasses

The following are optional for daytime outings,

• Laptop, because it's nice not having to use your phone sometimes.
• Water, this is optional because Konbini's are everywhere.
• Snacks, see above
• Bandaids
• Umbrella
• Extra pair of underpants
• Sweater
• Extra shirt

Activities

• Scuba diving. I had never gone suba diving before, and had a great introductory experience with Okidives in Chatan, Okinawa. I got a one on one session with Tony for 16,000 yen. It was worth doing.
• Bike riding. I rented a hybrid bike from 12.00pm to 5.00pm for 2,000 yen at a place called Shuhari Bike Works Okinawa. I got 10 minutes into my ride and the bike tire popped. I took it back and got the tire replaced without any issues. Once that was sorted, I rode from the bike shop to Katsuren Castle Ruins and back. Take this route on the way back to American Village if you want to coast downhill for several kilometers. It was really fun, definitely worth doing.

• Katsuren Castle Ruins. This was worth the bike ride.
• American Village. I have trouble finding food sometimes, so I usually go to malls where it's easy to find something to eat due to there being lots of photos and English menus. This is basically a substitution for a mall in that regard. It's just a big cafeteria. You can skip this.
• Toguchi Beach. The landing site of the Americans in WW2 was worth seeing. However, you might not be a history buff like me, or you might be totally mind broken from visiting countless beautiful beaches already. In any case, I stick to my advice.
• Former Japanese Navy Underground Headquarters. What are you doing in Okinawa if you do not visit this? Worth it.

Tips and Observations

• If you do not like busing, or walking, get an International Drivers Permit before arriving to the island so you can rent a vehicle here. I've walked over 15km each day I've been here.
• Bike rentals are expensive. Just rent them for half-days.
• Have a coin purse. This is useful for bussing.
• Convenient stores are everywhere. There is no need to pack snacks or water.
• For the coffee addicts, book hotels near cafes, otherwise you could get withdrawl headache.
• Lots of people here speak enough English for anything you need. Don't bother studying too much Japanese if you have more important things to do.
• Hotels can be booked a day in advance no problem. Ditto for snorkeling and other activities.
• The US Air Force planes in Chatan are LOUD. Do not stay here if you want to sleep during the day because the F-35's will wake you. I never noticed them in Naha.
• Most hotels don't support early check-ins, but they do allow you to leave your stuff in the lobby before the check-in time at 3pm.