Yeah, I completely understand the stress eating. I did a lot of that in the past, too
However, now I find stressing my body out by exercising more advantageous than eating badly when I'm upset. Plus, knowing that I pushed myself physically beyond limits I thought possible, and burning calories instead of consuming them, makes me feel much better afterwards! It's win/win
Now, unfortunately since I'm not a parent, I can't really offer much advice in terms of the situation with your youngest

I'd say the newly discovered hangover is punishment enough, but again, I've never really experienced one, so I can't really recommend that as a form of punishment - although I hear they're pretty bad!
It sounds tho like he's learned his lesson, plus he was upfront about it, so like silash said, that's good credit to him

He knows it was wrong, and wasn't even worth it in the end. Does he go to parties often? If so, maybe restrict his outings for a good while.
Also, is his birthday soon? Maybe you could also utilize the fact that alcohol and driving absolutely do not mix! Perhaps threatening and/or delaying his upcoming ability to drive will also keep him on the straight and narrow indefinitely!
Just some thoughts
At any rate, I'm sure you'll figure it all out and also get right back on track with your calories, as always, Tete
I have no doubt!
Best of luck with everything
