Backpack. Able to carry lunchbox and raincoat/jacket as per season. Also useful when wifey calls to get occasional groceries while returning from office.
Been using my Rynox Optimus S tank bag for the past 3 years, which doubles up as an expandable backpack.
Carried all sorts of stuff, weekly groceries weighing over 7-8 kilos and it never gave up.
For office, I carry my jacket, gloves, lunch box, power bank, cables etc with loads of space to spare and the expander takes care of impromptu shopping.
I can even carry my full face helmet once expanded.
Messenger bag but a better looking one. Not like the one shown here. Backpacks only when not driving to work as heavy load on one shoulder makes it stressful.