I carry sketchbooks, pencils, pens, watercolor kits everywhere. I use them daily, generating hundreds of drawings each year. Most are in sketchbooks using traditional drawing tools (pencils, paints, collage, charcoal, conte, etc.) or as digital files.
Sketch styles vary but the overall respond to the tone, message, and tools used to create the images. I don't think any one style can fit every story or assignment, so I work in a style that will best suit the subject matter, the context, or mood of whatever it is I'm illustrating, always aware of the page or project's overall aesthetic.