Any purchases more than $X should take more than Y days to actually do. And the higher the cost, the most days to think about it. Impulse buys tend to be bad financially and many of times are regretted, so if you wanted to buy a certain item on Monday, wait till Friday and see if you still really gotta have that item. If you are being honest with yourself, you'll know of you really need that item.

Another tip is to either buy everything in cash or everything on one credit card. Cash is obviously best since once it's gone, it's gone, but in today's world cash isn't convenient. So instead pay for everything kn your CC. Then st the end of the month, you know exact how much you spent and where it went. There's no question at that point because one of the hardest things to do is actually track everything - sometimes you forget to write it down, sometimes you lose your list, sometimes the value is written incorrectly. Well your CC will do all the math automatically for you.