First off, don't be mad at yourself! These situations are going to happen! Forget about it and get back on plan as soon as you can.
And, I can relate, as right now I'm off plan due to being sick. Some may think that's no excuse, but I came down with a bad cold just as I was doing my main monthly grocery shopping. I was achy, I couldn't think, I just wanted to get out of the store and get home to bed. Most of my LC food(ie, meat)is in the freezer until it can be cooked. I can't smell or taste anything, so I've just been eating those cup-of-noodle soup thingies in the styrofoam cups(in the pantry for storm situations)in lieu of LC soups(I just can't stand at the stove right now, just bundled up in my chair and DH can boil water for me). Plus lots of decaf tea. I'm at once dehydrated and bloated. I know I'm up a few pounds, but I also know as soon as I can spend time in the kitchen, I'll be back on track.
Things do de-rail us, but a bad situation shouldn't get in the way of our long-term success. I probably manage to be LC about 90% of the time, and I feel great about that.
The next time you are faced with a similar reception, hopefully, you will have some jerky or a protein bar in you purse for just that emergency. If not, just remember this is your main way of eating and you'll still be ahead of the game in the long run. I hope I'm making sense, as I'm trying to think with a head full of antihistamines, lol!