Just make sure that there are plenty of healthy options. If you find yourself eating mindlessly, you are way better off having a plate full of celery sticks than a play full of biscuits.
Also, remember that a knife is a very powerful tool. You can turn a 400 calorie cupcake into a 100 calorie dessert by cutting it into 4ths and only eating 1/4 of it.
And as Archimedes says, one day isn't going to make any difference in the long term. If you go a little over on one meal, it's not a big deal, as long as the rest of the time you are sticking with your plan.
"There's treasure everywhere." Hobbes, in Calvin and Hobbes