My three perfect add-ons
I have a Strada, with three bits o'kit to supplement the awful panniers. Love each:
Tankbag: Firstgear Monza. It looks like it was designed to go with the lines of the bike. Rain cover, clear top w/small front zippered pouch, no logos. Word of warning: magnetic holders can pick up small bits of metal that will scratch your tank, so keep them clean, or carefully remove the bag.
Tail bag: Tourmaster CRIII Nylon Sissybar Bag; 15Hx21Wx12D
It slips over the backrest, either on the pillion seat, or if carrying passenger, on the luggage rack that I built to bolt to the Ducati overpriced Performance joke of a luggage rack. It is really strong, but so small as to be suitable only as the frame on which to bolt a larger board (I sized mine for the base of the bag I had, and covered it with Rustoleum hammered-finish dark-grey, nearly matching the titanium finish, and it has proven very durable. I added a brake light bar to it, and the shiny, slightly upswept underside reflects my bright LED Rizoma signals, so it looks as if I have two on each side. Two Clearwater Darlas @2000+ lumens each light me up up front: visibility is survival!)
For more space I have a Fly backpack, which is awesome: roomy, rugged, well-designed, with a helmet expansion and more. It is spacious enough to stow my size 13 boots, and straps to the tail bag, regardless of its placement.
These items have seen me thru several months and about 12,000 miles of rain-, hail-, and wind-lashed desert and mountain touring, and a couple of graceless dumpings, and are as good as new. Hope this helps.