Well, for small stuff I use my tank bag, see picture 1. It is from MOTO DETAIL and was around 20 Euro.
With it’s 4 magnets it fits well on the tank and can be used as a backpack.
For the Helmet I have a small lock, stored under passenger seat, see picture 2, around 5 Euro….
With this I lock my helmet on the luggage rack.
Regards
Toni