Tickets: check. Passport: check. Underwear: check. If you've ever left the house for more than a day then you have a general idea of what you will need on a trip, so after you've double-checked the number of Q-Tips in your toiletry bag make sure you've left some of that coveted 50 lb limit for these items:
Sunscreen- yeah, yeah, I know- pretty elementary for a trip to the tropics, but chances are SPF is twice as expensive in Belize as it is in your neck of the woods. Use the cash you save to buy a couple extra cocktails with umbrellas in them.
Water shoes- on the Dork-O-Meter water shoes rank somewhere between fanny packs and pocket protectors, but trust me on this one. Whether fishing on the reef or jungle-trekking through mud, a good pair of "five-finger" shoes will be invaluable. I've sported these on the boat, tubing rivers, and exploring caves and it was well worth the "Look-at-This-Guy" looks I received.
Adventure camera- if you don't have a GoPro, it might be worth the investment if you plan on doing more than lying on the beach. Snorkeling, diving, windsurfing, zip-lining- these are experiences you'll want to document so that you can rub it in the farmer's tanned faces of your friends back home.
Map of Belize- remember that rolled-up Rand McNally your Dad kept under the front seat of his Oldsmobile? Well it's time to reacquaint yourself with the look & feel of a paper map. Cell signal in much of Belize is spotty at best, so don't rely on Google Maps. OK, OK- you could download the area from Google Maps and then use your device offline- but what do you do when your battery dies, smart guy?
Bug repellent- it's a well-known fact that mosquitoes can smell fair-skinned gringos from up to three miles away. Many of the Mayan ruins are inland and lack the coastal breezes that deter flying (and biting) insects. Again- you could buy repellent when you arrive, but it will be more expensive.
Cash- those of us who remember payphones and the Dewey Decimal System are probably familiar with "paper money." Credit cards are widely accepted in Belize and a lot of cards don't have foreign transaction fees anymore, but the Mayan woman selling woven baskets and oranges with chili powder (yeah- it's a thing) will not be impressed by your platinum status.
Patience/tolerance- you're not in Kansas anymore, Dorothy. Submerse yourself in the local culture instead of judging it. Resist the impulse to project your values on others while you're in their country. Loosen up. Your dinner isn't sitting under a heat lamp. It's being prepared fresh to order- at a Caribbean pace. Relax.
What are your Don't-Leave-Home-Without items? List them in the comments!