While the sender waits for your response to their email, take the sting out of your absence by involving them in a holiday survey, like the one below.
18. "Hi, you've reached [your name]. I'm away from [date] to [date]. If you need help with [X] before then, please contact [name] at [phone number]. Everyone else, please leave your name and number and I'll return your call when I return. Thanks and have a great day."

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.
It might feel strange to include happy client testimonials in your out-of-office responder, but doing so is easier than you think. A quick note that suggests they read the testimonials if they’re interested in a product or service you offer is an easy inclusion or postscript to your email. Just limit the amount you share to one or two.