I really want to wear a feather in my TOS. Maybe a big pheasant or eagle feather (maybe two) stuck upright over the left ear/temple. I am reassured at the number of folks who would admire me for it.
Traditionally, feathers in a bonnet are reserved for chiefs and armigers:

http://www.scotarmigers.net/pdfs/info-leaflet-2.pdf

Regards,

Todd