I don't have a copy of the play handy, but the quote must allude to a remainder biscuit and not a reminder biscuit. That would be a biscuit left over, uneaten, after a long sea voyage. The biscuit would be stale and hard, worthless. The hard biscuits sailors had to eat in those days were not much good at the start of the voyage. They were hard and tasteless. The leftover biscuit would be the worst of all because nobody wanted in, even though food for sailors was not abundant.