Going on our first cruise!! Any tips?

You're going to have fun in the cruise ship.

As for you excursions............sign up and pay for them now.  The last thing you want is to get on the ship, rush to the Reservation Desk to sign up for the Zip Line and Underwater Cave just to find them already full.  If there are any 'specialty' restaurants, on the ship, book those and pay for them now too.

Another thing to remember, no matter where the ship stops..............the towns are full of Jewelry Stores.

Mahogany Bay is a pretty name for a place is nowhere and far from what passes for a town so if you are going to go on an excursion do it at that stop. 

Getting to downtown Cozumel from the cruise dock is a long walk (I did it because I needed the exercise.) and you will find a pretty typical Mexican downtown. I wanted some high octane salsa that I can't get in the US so stocked up a supermarket (supermercado) there. If someone asked you to bring back some vanilla, it will cost about half as much in a supermarket as it will at a turista kiosk at the dock. This is also the place to buy your allowable liter of liquor. Tell the clerk "Yo tengo dollares" and they will cheerfully convert it to pesos. If you want bottled water buy it at one of the ubiquitous Oxxo convenience stores.  Put glass bottles and any food items it in checked luggage, not carry-on and safely cushioned by dirty laundry.

The tender in Belize docks right in town and the language is English so will be the best place to get a feel for the locals. 

Go on Google Maps and print maps of Cozumel and Belize City so you don't get lost provided you can read a map.  Print two copies because you will probably sweat a lot. 

Hopefully you guys are going a little latter such as winter or next spring. I feel like a lot of ports will only have a few things open if you go earlier but who knows. I have been on 4 cruises so I would say book the excursion ahead of time for the Belize part. I haven't been to those ports but I would also suggest cruise critic and looking up reviews for each report. Also make sure to select dining options early and make a request if you want for it just to be you two. Otherwise you will be seated with other couples unless y'all want that/don't care. 

Register with cruise critic.com.  You can then find the roll call for  your exact cruise, and "pre-meet" people who are on it.  We've met a lot of people that way, connected with them on the actual cruise, and have been friends with some of the people for years.  We are frequent cruisers, so now, whenever we book a cruise, we tell our friends and sometimes they book with us.

Also, as a new cruiser, you may be better off booking excursions through the ship, but more often than not, we book through third party tour groups as they can be a better deal.  Sometimes, people on your roll call will have set up a tour and be looking for other people to join up.  It's very common.  You can also look up information on the ship you are cruising on, like what specialty dining is available, demographics, that sort of thing.  And if you have a lousy sense of direction, print off a deck plan. Cruise critic also has pages and pages of information on ports.  It's a great way to find things, read up on them on trip advisor, and avoid lousy stuff.  

Carnival has fan pages on Facebook.  Not the "official" Carnival Facebook page, but unofficial ones.  These can be a great place to get information.  If you ask something like "What's one thing you would tell a first time cruiser", you will get all sort of information.  I'm not a member of any of the Carnival pages as I don't often cruise with them, but all cruise lines have them.  You will run into some cruise snobs, but who cares. 

But here are a few hints:

- Pack less than you think you'll need.  Overpacking is the hallmark of a new cruiser, especially shoes.  My wife and I can go 2 weeks with one rolling carry on and one backpack each.

- Make a spreadsheet with all the stuff you'll need. I travel a lot for work and pleasure, and have lists for different places, length of time, etc.  When I get back, I edit the list based on what I needed or didn't need.  Put EVERYTHING on it.  Things like toothpaste are easy to forget, and really pricey on the ship. 

- Bring snacks, like nuts, candy, whatever.  That sort of thing is also pricey on the ship.

- Bring over the counter medicines, like antacids, pain relievers, Neosporin, etc.  Again, pricey on the ship. 

- If you don't have one, get a portable charger for your phone.  If you do a long excursion, you may been it.

- I bring a wall plug with 4 USB ports.  Very handy when you have two phones, two iPads, a blue tooth speaker, etc.  I'm unfamiliar with Carnival's set up, but usually there's only one outlet in the bathroom, and one in t he cabin.  Newer or upgraded ships have USB outlets, but don't count on it. 

- Your suitcases fit under the bed.  Don't waste closet space with suitcases.

- You mentioned Cozumel.  We did an underground cave snorkeling tour there through the ship.  It isn't good if you are claustrophobic, but it was very cool.

- Be VERY careful drinking in port.  Don't be those people running to catch (or miss the ship) because they got hammered and lost track of time.  Search "pier runners" on YouTube for examples.  Don't be one of them.

- Wash your hands. A lot.  Even before coronavirus, there are occasional outbreaks of norovirus and other bugs.  I don't even touch handrails.  I've been n 19 cruises and never gotten sick

- If possible, plan on flying in to the port a day early, and stay in a hotel, especially if there is a chance of weather delays.  We did a cruise last year, and high winds grounded all the planes.  They were calling for similar weather the next day, so I cancelled our flight, rented a car at the airport, and drove.  

- If you don't have a drink package, pay attention to what you order.  You can probably view your account on the TV.  Do it daily to check for errors, and it isn't a bad idea to throw your receipts in a drawer. And do the math, maybe you don't have a drink package, but become aware that you would be better off with one than "pay as you go".  We generally get packages included in our fare.  Most cruise lines also you to bring 2 bottles of wine per cabin. 

- Remember, other than the casino, you don't use cash onboard.  Everything is charged to your room key, which is connected to your credit card, assuming you didn't do the cat deposit thing. You need cash in ports, and they all take dollars. 

- Make a Word document with all of your information, from flight times, airlines, flight numbers, your cruise confirmation number, excursions, budget estimates, etc.  Print it all and keep it with you. 

- Make copies of your passports and driver's licenses.  Very handy if you lose them, or get ripped off.  Highly unlikely, but possible. 

That's all I can think of at the moment.  Enjoy it, it can become addictive. 

The dock in Cozumel is a long way from down town.

I've been on several cruises to that area. Are you going in the fall? Summers can be very hot- you'll enjoy it more in the fall or winter. Definitely sign up for a snorkeling excursion at one of your stops. Or there's a beach in Cozumel where you can take a cab, rent snorkeling equipment on the spot, and snorkel off the beach. It's not as much fun as going out on a boat, though. Go on cruisecritic.com. There are reviews of the ships and the ports, and discussion forums where previous visitors post tips and information. 

I love Carnival cruises. There's always a lot going on, and you can choose the activities you want to do, whether it's trivia contests, or karaoke, or just listening to music. Have a great time!

BTW, people are likely to post telling you not to go. It's your choice, of course, but if your fiance has been working with COVID patients, it's very likely that he's been exposed, and you have, too. If we ever get some decent anti-body tests, you'll be able to know for sure, but there's a good chance you've already had it.