Many writers are picky about what they use to write with, i.e. writing implements and paper. I am too; luckily, I don't need anything particularly esoteric. My preference is to write with a mechanical pencil (HB lead or something medium soft, point size doesn't matter too much). If I've got to write with pen, I like a Bic ballpoint. I have a fancy pen that I received as a present, but it doesn't write very well; it has a lot of drag, the ink doesn't come easily.
I'm not sure why I prefer to write with a pencil, since I almost never erase anything. Rather, I'll cross it out if I decide not to go with it. One advantage to that is that I can see what I originally put down. Maybe it's the idea that I could erase, if I really wanted to.
A mechanical pencil writes quickly and easily, as long as the lead isn't hard and scratchy. One drawback with a pen, at least with the way I write, is that it tends to get less legible, because when writing quickly I sometimes won't take the tip all the way off the paper, and there will be a drag of ink connecting letters or words.
I like notebooks with ruled paper. Not spiral-bound; those are icky, the spirals are inconvenient, take up space and get snagged in things, and there are those little strings of torn paper that get everywhere. I've used Moleskine journals and liked those; they're a good size, and the string around it is convenient. (Cheaper journals with the same design are good too; I got a cute one with bugs on the front of it. Come to think of it, I don't know that it was any cheaper. But it wasn't a Moleskine. Moleskines have pretentious points, too, because they were supposedly used by various famous writers and artists, I can't remember who.) That way the notebook won't get stuff wedged between the pages or bent out of shape in a bag, and a pen between the pages won't slip out.
A notebook I really love is a Miquelrius "Leather-Look Pad". There are many pages, probably at least 350, but densely packed--the spine is maybe 3/4 inch thick--yet the pages aren't thin or flimsy. It has such a nice hand when you open it; it feels very nice to flip through. The cover is fake leather and sturdy, and protects it from water and such. They come in various colors, and in "squares" (graph paper style) or ruled. I just wish that the ruling was a bit more narrow, because I could write more lines per page.
Writing utensils can be a big deal, if you do a lot of writing (and are anal, neurotic, and/or just picky). My mechanical pencil ran out of lead in a cafe, and I was very upset. I started surreptitiously looking at the writing implements of people around me, in case anyone had a mechanical pencil with 0.5 lead that I could borrow. Finally I just wrote with a Bic ballpoint. :P
Okay, we've got a general word for "thing you write with;" you can say "implement" or "utensil" or something. So what do we call the paper? "Medium" or something? In any case:
What are your preferences with writing implements and... media? How important is it that you have Just The Right Pen?