A top box on a m/bike is no big deal, but I think all two wheeled users should be wearing florescent jackets anyway.
When I was doing my M/C test, I was taught by an ex White helmets display team member, who at that time trained the police bikers, he told me why I should always wear florescent clothing.
He said imagine you're driving a car on a country road at night, you drive down a long straight towards oncoming car lights & feel a bump, it could be an animal OR it could be a black clad biker lying in the road after an accident!
I also think that cyclists should have a registration plate on their bikes to stop them running red lights & damaging car mirrors, it should be compulsory to have flashing lights front & rear to aid visibility.
I treat cyclists & other vulnerable road users with the same care that they show for they're self preservation, if they wear bright gear & are riding/walking sensibly, then I do everything I can to pass them safely but if they don't give a damn for they're safety, why the hell should I!!
Phill