I would say about 1k - 2k. But it's not a big deal if you run out of food because the bot will go to the bank, and log you out. It doesn't just keep fighting until you die.
At least Autofighter pro does this, I don't know what auth you have though.
I'd use Lobsters, they're cheap, and do the job. Just buy 10k of them and experiment on how long they last you.
AutoFighter, as said before, if there is no food in the bank, will log you out.