After losing the food to the sharks Cody states that a human can survive a week without food. While he correctly also states that water is more important, a human can in fact survive up to 40 days without food, it is water that human can only survive 1 week without. Given that he is good student with good grades he should know this.
After Ms. Tuttweiller gives London her clothes back, the wide shot reveals they left the blue spot marker tape on the ground and/or panned too far down, in front of Tuttweiller.