I'm not going to break this one out, as you can see from the picture you just need dark/black clothes (sweats are a Halloween staple), and a 'broom'.
Wouldn't one of those swishy ones, like a specialy Swiffer broom, look similar, if you get it black? Or an old wood/bristle push broom about 8" wide.
For the hat use an old baseball cap.
You can always pin a picture of Mary Poppins on your breast.
Here is a vintage piece of sheet music, with a great CowGirl illustration to inspire all you Cow Girls out there...