When I first got to Japan in 2000, I figured my days of impulse buying were over. Little did I know, it would be even easier with internet shopping. Instead of actually paying for something, all I had to do was click "Add To Cart" and it was mine.
Now that I'm back overseas again, I've been pretty good about keeping the internet shopping under control. One thing that helps is the Amazon.com Wish List. Instead of adding something to my cart, I put it on my wish list. I let the list build up over several weeks, and then buy everything all at once. The difference is that before I purchase, I go through the list and make sure I still want everything. Often, something I couldn't live without turns into something I really don't need.
By the way, this also works with my iTunes shopping cart.