I recently described myself as being “out of the virtual office.” Away from the virtual office” would probably have been even more precise. I think whatever you say, people will understand what you mean.
We promise the world will not end while our offices are closed and encourage you cherish this time with your families and friends!

I will be out of the office starting (Starting Date) through (End Date) returning(Date of Return). If you need immediate assistance during my absence, please contact (Contacts Name) at (Contacts Email Address). Otherwise I will respond to your emails as soon as possible upon my return. Thank you for your message. How do you respond to holiday greetings? "And (also) to you!" You too! Thanks, same to you! Happy New Year to you and yours (when you want to extend the wishes to the other person's family) How do you let clients know you are going on vacation?
Then there was the occasional one who would do what Alison mentioned with the sickness excuses, and create a tale that read like a police report: “I must miss my deadline because, on the night of August 12, my 45-year-old sister was alone in her house when an intruder entered. He was a 6’1″ caucasian male wearing a black balaclava and carrying a candlestick. As my sister approached him, with the dog barking around her heels, she heard a distant car crash which led her to have a fatal … etc.” (This is not an actual excuse I received, just similar in detail to some of those that were submitted.) These ones I was pretty sure were a writing exercise, requiring time and effort that could have been put to better use on the actual assignment they had been given.