To survive in the Costa Rican rainforests, one must be prepared for heavy rain, insects, and poisonous plants while regulating body temperature. The document outlines dangers like hyperthermia, dehydration, and infection that can affect the respiratory, circulatory, and digestive systems if proper precautions are not taken. It recommends bringing long sleeve cotton shirts and pants, a wide brim hat, mosquito netting, gloves, ankle boots, insect repellent, water, food, and navigational items.