I'm not sure I can narrow it down to just one thing. The very top of my list is my Martelli Ergo 2000 rotary cutter. LOVE, LOVE, LOVE that cutter. When I helped out at my friends quilt shop, I took my own cutter. #2 on the list is my Tutto rolling bag and serger bag. When I go to retreats if it doesn't fit into those two bags it doesn't go. I'm really surprised at how much use I get from the serger bag, I had to be talked into getting it. #3 the vibrating pillow -- although there's got to be a cheaper version. This is not so much for me, but for my husband. He's worn 2 of them out!