Mirror?

Map case or some kind of handlebar clip system for your cue sheets? (I just ordered the Detours Digi Midge for my road bike. It's tiny but incorporates a small clear window on top for tucking in a folded cue sheet....Detours appears to have a nice range of small, sturdy bags to help keep things handy on a stem or top tube.)

Lights to make sure that you're highly visible to traffic?

Small horn or bell?