Full disclosure, I am writing this mostly from memory (on Sept 3 2018) as I explore returning to Belize. Belize is easy in that the official language is English and if you know some Spanish too, you are golden. The Belizean dollar is pegged 2 per 1 US dollar and just about everyone will accept USD instead of BZD; pack small bills.
Most airlines will require you to get to Belize City (Philip S. W. Goldson International Airport) through Dallas or Houston. At time of writing American Airlines and United Airlines offer round trip from Denver to Belize City for $800 during the first week of January.
There are a variety of rental car options and we ended up renting something close to a Land Cruiser, making it easier to traverse the country at our pace.
You can stay at the Belize Zoo and get a night tour!
Right before the rounabout to Belmopan, there is Guanacaste National Park on the North side of the Western Highway; for a few hours of rainforest hiking.
Grab groceries in Belmopan, at a place like The Mall, if you are looking for the easy American grocery store experience. Complement that with a farmer’s market in town and you will be good to go for days. Most of the big grocery stores seems to be run by Han Chinese?
Stayed at https://www.bananabank.com/ for a night while hanging around Belmopan.
Pay a few dollars to check out the Cahal Pech Archaeological Reserve. It sits on one of the hills in San Ignacio has a great interpretive museum and outdoor Mayan excavations.
Xunantunich has to be some of the most imposing Mayan pyramids I have seen in person.
We stayed in the Lower Family Suite at the Maya Beach Hotel and Bistro. The hotel has a collection of activity gear that we used every day. I love kayaking and heading North to the next marina on the coast was quite the adventure.
The pub grub and drinks just down the road at Mango’s was solid.