starvation is a horrible way to die.
i would suggest seeing a therapist to see if you can get the voices to stop, or at least quiet down a little. i don't know you, maybe you've already tried that, in which case:
if possible, i would reccomend trying any other way, the big 3 being SN, inert gas, and/or partial hanging. if you can't buy things, is there anywhere you could jump from taller than 10 stories? anywhere you could drown? you could try getting hit by a car/train if you don't care about traumatising people.
if not... i wish you luck, and i'd wish you peace, but the next week or so when you start the attempt will be everything except peaceful.