If you secure place (using the little gap beside the obelisk, so it will not even hit you till after it burrows) you won't require much food, if any. Guthan's probably would not be very efficient. I recommend you utilize a broad/emerald (e) setup, start with RS gold the emerald (e) to poison, switch to broads to complete it off. Each kill is worth roughly 20k or so. I myself do 2 kills each run (using eagle eye and prot melee occasionally ) then home port, recharge pray at altar, use fally portal, bank and go back in time for the next spawn to happen.
Hey. Everyone differs. Is there really a"right" way to kill something? In my opinion, simply hit them with your best weapon and equipment, while fostering! But then again, I have never killed one. Just cancel what's hardest and/or what annoys you. Why keep a task that is slow? I would cancel Black demons. Heard those are poor. Kalphites are quick and will get you a few fast slayer points. Not automatically...