A friend of mine, who has been knitting for YEARS, finally picked up a ball winder.
For those of you who haven't used one, they help turn a skein of yarn into a little yarn cake. It stays neat in your knitting bag and you can pull the yarn from the center of the ball, so that your cat isn't as tempted to try to fish the thing out.
I love mine and consider it absolutely needed knitting equipment. The plastic model here may not look like much, but we use ours daily in the shop, so you know it will hold up to one knitter's use.
Winding by hand is nice and all, but I'd rather be knitting! What do you consider your basic knitting tools? Yarn, needles, darning needles, ball winder, swift....