The rash guard is critical for protecting you from the blazing Indonesian sun. Your skin will burn very badly unless protected well from the sun. Wax is hard to come by in Bali. You don't need much as far as clothing goes. However, in the dry season from June until September, Bali does get a bit cool at night and you might want to have a long sleeve shirt or two just in case.
Hats are a very good idea as well and so are really good sunglasses.
Bring very good quality sunglasses to Bali to protect your eyes from the sun and wind and make sure you bring an extra pair and also bring a leash for your sunglasses. Sunnies dropped overboard are usually gone for good. Although there are very few mosquitos if any around the boat at night, the same does not go for land. Mosquitos and Malaria are a reality here in Indonesia and if you are on land, you need to take precautions against mosquito bites. This means highly effective mosquito repellent and a good quality mosquito net.