A lot of people don't stop to think before they make a purchase. They see it in the store and say, "I want that." They then proceed to make the purchase, and soon after they get it home they realize that they didn't actually need it or want it. A lot of times if you just wait a couple of weeks before making a purchase, you'll find that you won't actually end up buying the item.
If you decide that you want to buy the item, why not try to find a better deal online? A lot of the times you'll be able to find a better deal by looking for coupons to online stores such as amazon.com or overstock.com. If the item's worth a good amount, do a little research online to see what other people are saying about it. Sometimes you'll find that the product is completely worthless and not worth a single penny.
Basically what I'm saying is wait a little bit before making a big purchase. You'll save money in the long run and become a smart shopper at the same time.