Online buying guide
Before you open the online website for buying items just try to note down / remember the things you would like to buy and possible sum that you would pay. Give only 10% of total for the unplanned for buying unplanned item.
Do not buy during sales offers because there is offer. If an item is in your wish list, and the offer price is below the standard price of the item, then only buy. Else do not buy. There will always be sale offers. Need comes first.
If you would like to buy something, and there is no urgent need write it down on a wish list, and wait for sometime, a month or two.