I think a good idea would be to ask stuff like "What's the weirdest/funniest/scariest thing that's happened to you?", the question is vague enough so everybody can participate and it can sprout some great stories. As well as stuff like "What would you do if tomorrow was the end of the world?", or something that's a little bit more specific and less extravagant like "What's your favorite movie/book/game and why?".