You know the way your mind latches on to something that you think you need or just want to buy? And then it starts painting an exciting picture about owning this new thing, and your ideas and feelings start dancing around with each other in your mind. It can become pretty hard to pull yourself out of this. Often, out comes your credit card and you make the purchase. Here's what I do to stop this, and it works at least 50% of the time..
I ask myself, "how could I re-organise or rearrange my life (or make better use of the things I already own) such that I don't need to buy this?" This question puts my attention on what I already have and can control to try to meet the needs or purpose of the thing I'm tempted to buy. I often surprise myself that I can meet the needs of the tempting purchase with something I already own. Even if it helps delay the purchase by a few months. Or, I can rearrange my environment or put myself physically in a different position such that wanting that new thing becomes irrelevant or less desirable. This is all about squeezing more value out of the things you already have, and I don't think people do enough of that.
For me, that question is worth a lot of money. I hope you find it useful.