A caveat if you haven't already purchased ...... don't go for high thread count sheets. They are way too hot for this climate.
Recommend 350 at most. If you like fancy, I recommend the birch-satin sheets from BB & B. They are soft and lightweight and just about perfect for the tropics.
Great deals on nice towels can be had at Mirab in Belize City. Towels are so bulky I cannot imagine packing and flying them in.
Pretty sure you need cash (not credit cards) for customs so be sure to come prepared.