Water shoes as the rocks can be slippery Cash for the bus, park admission, food/drinks, hotel, and shuttles - credit cards aren't accepted Your camera with a waterproof case such as a GoPro or a waterproof phone case. A padlock so you can store belongings in a locker securely and avoid lugging everything throughout the day A waterproof flashlight or headlamp if you want to explore the caves more thoroughly If you have special diet restrictions you'll want to pack food as vegan and other options are limited