Along with everything else people have already said: something you do in your spare time which shows some level of motivation. Hiring/firing managers I've spoken to in the past have been very, very wary of hiring people who either don't list any hobbies in their CV, or in interviews reply to "what do you do in your spare time?" with "just watch TV or game". You don't want to be seen as that person who has nothing to talk about but work when everyone is out for a beer after hours.