Good luck! If you can't think of an answer, you can always say, 'sorry, I'm drawing a blank, can we come back to this?' and move on from there. I've done that and it's been fine.

I try to act as if I am at a party or hotel bar meeting new people (which is weird because I hate meeting new people at parties). The more practice you get at interviewing, the better, so it's awesome that you have two scheduled in one week!