My opinion is that a good writer can and should be able to write anywhere.
This, however, doesn't apply to me. I have a certain corner, the only place I write, with my reference books, laptop, numerous note-pads and pencils. I do carry with me small pads and pens for notes and also I have Evernote in my cell and E-pads, but these are for note-taking. More serious (!) writing takes place at my corner.