Ride it for a bit until you know what, if any, additions need to be made for your own comfort, seat, bar risers, screen, mirrors etc.
Once you're happy with all that then you need panniers, back box & tank bag...maybe? Or, if you won't have a pillion some folk like a waterproof roll bag on the pillion seat.
My preference is hard panniers, easier to fit & remove & more secure. Loads to go at just do your research.
I'm with Hugo on the packing. It's surprising how little clothing you can get away with, most places you will stay at will have a sink & water for washing. Get some decent base layers, the lightweight, quick dry stuff are great IMHO. Bit of a rinse with 'all purpose' soap, hang 'em up & they're ready to go next morning. Anywhere you will go, just about anyway, will have shops to buy anything you didn't take.
A bottle of water.
Start with a credit card & a toothbrush & go from there.
Perhaps breakdown insurance....buy it & there's a good chance you won't need it....don't buy it & you may well wish you had.