Well, for the most part, I don't consider making the choice to indulge in some not-so-healthy foods and drink to be a "bad" day --- just a day where I chose to eat at or above maintenance, knowing that it is the sum of all of the little things that will have more of an impact than the choices of one day. Realistically, even 3500 calories over maintenance will be balanced in a week of eating in the range to lose 1 lb per week.
That said - it's been a loooong time since I had a hangover, but I would do the same thing now that I used to do: eat lots of honeydew melon and cantaloupe, lightly salted, and drink some broth (both needed to balance electrolytes and re-hydrate), and drink lots of water, and eat very lightly (I seem to recall plain scrambled eggs and a bit of dry toast being my go-to). I used to include some light activity (a walk or swim) and an extra nap. After a day of gentleness to myself, back to normal!
Really, it's just a part of normal life, and not worth worrying about. Be glad that you enjoyed the holiday, try to remember in future that hangovers suck, and have yourself a great rest of the week (once you feel better)!
Sir Terry Pratchett:
"Science is not about building a body of known 'facts'. It is a method for asking awkward questions and subjecting them to a reality-check, thus avoiding the human tendency to believe whatever makes us feel good."
Starting weight: 258 lbs
Maintenance Range: 147-155 lbs