I like to carry this little helmet lock that I keep tied to my handle bars. My other gear is rather plain and entry level. I have a nice Kriga tail bag, but my new MC does not have good mount points for it :(
Looks like Hepco & Becker make racks for the XSR900. I considered them for my 919 quite a lot but never bought them.
Then you could easily strap your bag.