My advice is to take good footwear and watch every step you take. The entire island is nothing but a giant lava flow covered with thick vegetation in many cases. That vegetation hides a considerable number of "booby traps" that will try to cut you up, twist an ankle, or break a leg. You don't have to take your most expensive waterproof snake-boots, as you could easily ruin them in the lava,...but good hiking boots that will protect your feet are a must in a lot of places there.