Get to the point where you are able to fight Lesser Demons or level 54 Skeletons or Red Spiders. After defeating the Dragon, or at least using the secret door the first time from the Crandor side, get enough Fishing and Cooking to be able to catch and cook Lobster. Bring a Lobster Pot, a Tinderbox and a Hatchet (any type). Reach the island from Karamja (through the secret door). Fight your monsters, etc. When you run out of food, return through the secret door to Karamja and fish for Lobsters. Then, cut a tree for logs, set it on fire, and cook your Lobsters. This allows you to survive in the Lava Chambers under Crandor/Karamja Islands almost indefinitely. This is useful for leveling up against certain monsters and to also get a lot of one kind of item from a particular monster (such as Rune Mediums from Lesser Demons).