"Get a separate prepaid card that you can dedicate to purchases in the chosen category. Emboss the card with the category name, or just write it on the card with permanent marker... since it’s a prepaid card, you can’t overspend on your habit. When it’s gone, it’s gone. There’s no credit available beyond your budget, and there’s no risk of overdraft — just a humiliating decline if you try to exceed your budget."
Check out the rest of this great tip here: Blog.FamZoo.com
-------- PS: This also works with gift cards to certain stores too. Say, like Starbucks ;)