drink lots and lots and lots of water. consider going back to induction levels for a few days to get right back into ketosis.

climb back up on the wagon. let it be just a one-meal cheat, not a week-long binge.

You said that you didn't plan for this event. Time to come up with some coping strategies so you won't be caught unprepared next time, anytime.

and be kind to yourself. things like this are going to happen occasionally. It's not the end of the world! Keep going!

cheers,
RealityS