Bullet journals for work and for life. Gospel reflections. Letters to friends. Shopping lists, crosswords, notes from phone calls, diagrams. About the only thing I don't use it for are things requiring a pencil. Would you like to hear about the world of mechanical pencils? 😀
The Lamy 2000 is a great choice as others have said. A slimmer, less heavy option might be the Parker Sonnet. Make sure you get a genuine one from a reputable dealer as knockoffs are everywhere.