Take two potions for prayer, 4 anti-poison potions (you'll need them with all the protect prays you need), and 1 super energy (you don’t want to OSRS Gold run out when traveling on the street). Cammalot teliportation ranes can be helpful in the event that you do not take your food in.
For the underground part you will need 4 prayer pots, 4 super-energy potions, two potions to prevent poison, the items needed for the quest, and then the rest with food (if you keep protect from mellee on all the time, you will do fine). Be on the lookout for your run. When it reaches 50%, consume a small amount of energy from your run. When you reach 28%, you can take a prayer potion. Consume food as you need.
To aid the demon an anti poison (for after the fight, when you get teliported into the middle of the forest) and a set of camalot teliportation runes (for following the battle or in the event that the demon is able to survive: cute:), 4 prayer pots (over kill, but better to be safe than sorry) and the rest with good food.
I recommend bringing range equipment (I utilized 10 mitharrows against him at 61 ranging, it was boring of waiting) as well as a short bow that is magical! Anything that Buy RuneScape Gold gives prayer and/or magic defence is great!