Humor, yoga or spending time with family. However you blow off steam, make it positive and not suggest that you fall back on bad habits when stress gets to you. Skip saying you don't have any work stress because we all do. Tell the interviewer that you understand the pressures of the job and that you have experienced similar pressure before.
"To keep from bringing work stress home with me I like to run outside during my lunch breaks. The fresh air and excursive helps me clear my mind and give my very best at work."
Second Answer Example
"My work stress is kept at bay by a well-balanced diet, exercise and 8 hours of sleep."