I would probably say that if your counter is correct, and you are five days into it then going off the wagon for just one meal would probably be a fairly significant set back.
But... if you are determined to do so, I would suggest that you get something you really really REALLY do not like. Something that you have to hold your nose just to choke it down.
You see... speaking from my own experience, I would sometimes put myself in situations where I "just had to" go off the wagon. And...OH... since I am off the wagon, I might as well eat something really yummy... and a lot of it too... After all, I went this far.
So, if you HAVE to go off the wagon, try not to enjoy it. It should show you where your motivations are.
(And, I am not saying that you can't enjoy food. There's nothing wrong with planning a treat for yourself. But you should not be enjoying these unplanned "mistakes")