In support of my immigrant brothers and sisters in Colorado, I didn't buy anything for a whole week this past week. It was an interesting experience which I would recommend to others (do it as a test of self will).

Several times I had an urge (more than a simple notion) to stop and buy something (e.g., coffee, food) although there was nothing I had to have. I had plenty of food at home. Notably, the urge was much stronger if I was driving my car, than when I was just walking. What is the psychology of this urge?