i absolutely hated Uni assignments. I procrastinated, drank beer, got extensions,did everything at the last minute and crammed like you wouldn't believe. i remember even feeling like a toddler would having a tantrum because I felt like I couldn't do it - but I did. I made it in the end and I'm doing ok now.
i only have a four year old so I can't really comment, but I'd leave him to it. Tell him you're there if you need him, but it's his journey. He needs to know the consequences of slacking off, and if he gets it done and passes good for him. If he's going to be a little princess and not want his sandwich don't offer again, he can make his own snack as long as he knows there's enough good stuff in the fridge.
he can't have it all, including going away for a week with known responsibilities. I'm sorry if I'm niaive to potential mental issues (what does he mean by "wants to be gone?") but it sounds like he needs a kick up the bum