That cylinder is a portable compressed can to fill a flat tire, it's a fix-a-flat. I got it like that. I probably won't use it.
It looks like, after looking at the frame and motor number ranges, this bike is a 76. What is more sought after, a CB 400 Four F model 75, 76, or 77? I thought it was a 77 because it was registered as 77 in Italy, that's the year it was first registered.