chop up your credit cards or decrease the spending limit on them.
carry around cash.
get other peoples opinon when looking onlione (ie. older sister.. they might say that item is ugly and you shouldnt buy it)
look at the website and add stuff to your shopping cart. comeback after a week and if ti's still there then buy it (i tend to do that on websites and when i finally want to purchase it, it is all sold out)