Rum is cheap and good in Belize.
Wine is expensive, but there is a lovely selection at Wine de Vine, and you may find an interesting selection that would not be available where you live. They also feature some great sale items. I'd recommend stopping in if you are a wine fancier, as it is a lovely spot with excellent products, including gourmet meats, pates and cheeses.
Other hard liquors are quite expensive (average of 2X's what you may pay stateside).
The GOOD news is that at the international airport, right by the luggage carousel there is an incoming duty free shop with premium products at excellent prices. Much easier than carrying the goods, unless you need tons and tons of adult beverages.