Currently reading - Kitty Goes to War by Carrie VaughnThis is one of those subjects that takes the concept of "subjective" to the extreme. So please take what works for you and discard the rest.
Much of what a writer considers equipment depends of personal drafting preference. Neil Gaiman uses a blank journal and a fountain pen to write the first draft of his stories, whether they be novels or screenplays, in longhand. Frankly, I was a computer jockey for too long, so my typing speed is way closer to my thinking speed. I've tried Neil's method. It drives me bonkers.
Pens and notebooksEven if you don't draft by longhand, or shorthand for that matter, you'll need something quick and handy to jot down that flash of inspiration. (Really, does anyone actually use shorthand anymore?)
ComputerMore and more agents and editors are accepting queries and submissions by e-mail. (And some, only by email!) You don't need a machine with a lot of bells and whistles. A decent brand-new notebook can be had for $500. If that's out of your price range, check with a pawn shop. Free e-mail accounts abound, but be aware they come with a lot of spam.
For word processing, the industry standard seems to be Microsoft Word. If you absolutely can't handle the thought of givnig Bill Gates more money, make sure your word processing software can save a file in RTF (Rich Text Format).
PrinterIf you can afford it, I highly recommend a laser printer. Ink printers are fine, but what happens when the postal carrier drops your opus in a puddle? Yes, the inital outlay is greater, but a terrific machine can last for years.
Wait a minute, you think. She just said that practically everything's done electronically these days.
Yes, I did. I can count on two fingers the number of agents who requested anything from me by hardcopy in the last year. But there's a number of other uses for a printer besides spitting out manuscript pages. Labels, bookmarks, business cards, etc.
Extra Ink/Toner CartridgesYou're printing out pages for your critique group, you're already five minutes late, and oops! There goes the red light saying you're out of ink/toner.
Tyvek EnvelopesSeriously, nothing beats these puppies for durability when you do have to send a manuscript by snail mail.
PostageIf you live out in the boonies, keep an account with
the U.S. Postal Service. Even if you don't, an account is so much better than standing in line at the post office. You can order supplies, like shipping labels, online too.
Reference BooksAt least have a decent dictionary and thesaurus on hand. A copy of Strunk & White's The Elements of Style for grammar brush-ups is a good thing to have also.
These are what I consider the must-haves of any writer. Anyone else have something they'd like to add?