I actually have shopping rules. When I buy clothes, I have to buy a pair of jeans and matching top. Can't buy one without the other. My mother finds it quite annoying but I'm anal about it. I usually don't plan what it is exactly I'm going to buy but I usually know what I want as I walk past it and I justify my reasons for the purchase in about half a second in my head. (eg. "Man, 2 Fast 2 Furious sure was a cool movie..hey look Need For Speed: Underground! *buys*)