Cosplayers, seamsters and quilters: What would you use in your "sewing survival kit"?

I am making a “portable sewing survival kit” which will consist of a messenger bag with a number of built-in features for sewing supplies. I’ll be carrying this around at conventions as a way to keep a handy supply of costume-repair itms as well as things I pick up at the con.

I’ve already decided that I would have a place for scissors, a seam ripper, and a built-in pin cushion. In the convention aspect, I would also have a pocket for a camera and cell phone. My question is, what other features (especially sewing-related ones) would you want to have in such a bag? Also, where would you have them – in the innermost area or on an outside flap?

Thanks all!