The following exercise is from Dieter Broer, a scientist of biophysics who connects science and spirituality. Before you buy something, ask yourself 3 questions:
Do I really need it?
What for do I need it?
Could I wait a little bit longer before buying it?
With these questions you can become aware if you really want and need something, or you would buy it out of a reaction or pattern, i.e.: “I need to buy something to feel good”, “I should buy another CD”, “this object will make me feel better”, etc.