been there. fight the urge to stuff everything you see into your mouth, it'll work against you, but DO eat today with a target of something like 70% carbohydrate, 15% protein, 15% fat.
I dont know the physiology behind it, but when I feel as you're describing, it seems like I crave sugar (more than I normally do) and am thirsty. So, I do best when I'm feeling this way by eating something every couple of hours that helps with both sugar and thirst, like an apple, orange, peach, etc. Also, if you didnt eat for a long while, I'll also bet you didnt drink enough water and have hydration deficit as well as caloric deficit. drink water, juice, gatorade, stuff that tastes good to you and can help you get the hydration, calories, and sugar levels balanced.
Good luck, and if you dont do well this weekend, chalk it up to learning.