Essentials: Rotary (Olfa) cutter, 18x24 cutting mat (though I would LOVE to have a bigger one!), a loop turner, my 4x8" Omnigrid ruler with 1/8" markings, and my inherited gold thimble which is the only one that I have found that fits.
Could have done without: A 9" circle wedge ruler. I have used it - just doesn't fit into my game plan very frequently.