Okay how about telling them your not really hungry kind of full from earlier in the day. They don't have to know it's just juice that made you full. How about saying your tummy isn't quite feeling up to food. This is true because you never know how sudden food after fasting will affect you.
If all else fails eat as clean and healthy as possible. If there are veggies and fruit stick to them.
Try and concentrate on the people and have a marvelous time. Keep on going!