I have certain essentials for writing. They are slightly different depending on what I am writing but they nearly all centre around music. I use music partly to block out distractions but also to pull me into whatever I am writing. The novel I finished recently was written entirely to traditional Irish songs, mostly instrumentals played on the harp or panpipes, but sometimes vocal versions. The tunes varied from jigs and reels to slow sad ballads but in some way they tapped into my mood and the story I was working on. Whenever I tried to introduce some other music I would lose my rhythm and it became much harder to tell my tale. I'm now well into the sequel and still using the same music in a continuous loop on the computer. Whenever I turn it on I'm immediately transported to this imaginary world and I am ready to write.
For short stories I like variety. It ranges from musicals ( my current favourites are Hair, Jesus Christ Superstar and Chicago), Country & Western artists specially Johnny Cash, rock in many of its permutations from when it started to the present day, popular music, Scottish traditional music, bagpipes, Andean panpipes, Greek traditional music, Gregorian chants, Abba, folk ... I could go indefinitely. As you can see my taste is very wide ranging but once I have the right piece of music the story flows onto the page.
I tackle non-fiction differently. When I am working on something factual I prefer instrumental and usually opt for something quiet in the background.
Poems are the exception. They tend to come from things I feel very passionate about and I don't want the distraction of other ideas or anything that interferes with rhythm so I tend to not have music on at all when I'm working on a poem.
Thinking about this has made me wonder about how other writers work. I'd love to hear about what are the essential things for you.
BTW I have a rousing version of The Boys of Killibegs on right now.