+1 on the fenders VNA mentioned.
I keep a baseball hat in my bag for the rain. I wear it under my helmet, keeps the rain off my glasses so I can see.
Also turn on your lights, as cars cannot see you so well with their wipers going..or if they work well.
I also keep a saddle cover velcrod under my saddle I can pop on when it rains. Don't want to wreck my brooks.