Rachel,
I am the SAME way. A lot of times I will go because they are having a great deal and then I get there and I think what am I doing here I have enough fabric at home for this quilt, and that quilt and I walk out with nothing. I wouldn't go into a store and buy paint if I didn't have a wall to cover, I wouldn't buy diapers if I didn't have a butt (just turned a year old) to cover. Why go in and buy fabric if I don't have a quilt to make with it!
When I do get ready to make a quilt I buy everything I need for it right then and there.