Scott,
As someone who conducts Filter Interviews, I may be able to help.
First of all, previous posters are spot on when they tell you to be yourself.
Secondly, don't lie; we will find out one way or another! (Think security check, references etc)
Thirdy, don't worry about Current Affairs at this stage and just concentrate on your knowledge of the RAF and your chosen branch(es).
Fourthly, the background issue is just to find out a little bit more about you as an individual and whether there is anything in your (recent) past that may prevent you from completing, or distract you from, training.
Finally, you appear to be doing the right things and should make sure you sell yourself but without being too big headed.
Good luck and remember to practise.