Long pants are a necessity in the jungle. Insect repellent is useful during jungle hikes or when the air is calm along the coastline. Film, batteries, cosmetics, health and beauty aids, and snack foods are expensive and brands are limited. Drinkable water is generally not a problem. No adapters necessary for U.S. appliances.
Some remote hotels have electricity furnished by generators.
A valid passport is required to enter Belize. U.S. citizens don't need a visa. Citizens of other countries should check with the Belize embassy in their country for regulations. When leaving Belize, you must pay an exit fee. This is a good time to get rid of your extra Belize dollars.