I carry a spare helmet shield in the plastic baggy they come in, either Blue iridium or clear depending on whats on the helmet.
Cigs, lighter,meds,maps, wallet, I-River 20 Gig mp3 player w/ remote, charger for cell phone and mp3 player,usb cable,MotoCom SB-1 amp/intercom unit, S100 detailer/wax, microfiber cloth, spare hearing aid batteries, hearing aid storage pouch,spare AA batteries and Listerine breath tabs,spare key for the Feejer and all my house/car/work keys. Magnetic bag hasn't caused any problem with any of the electronics yet.
Various other things go in the Oxford sport tank bag when needed, never had to expand it yet. Above items are always in there if I'm traveling more than 2 hours one way, otherwise it stays home and the essentials end up in the pockets of the JR mesh jacket, same if I know I'll be leaving the bike unattended for extended periods.