From my personal experience as well as from the experience of many of my friends I can say that there are three common areas where spending can get out of control. I am thinking here about shopping, eating out in restaurants as well as traveling.
It is true that when I go shopping, I might be tempted to buy things I have not even thought about buying before entering a store. the same applies to restaurants and travel. Every time I want to buy a holiday package to some destination, I am tempted to spend more money on a better package and travel to some holiday destination instead. Sometimes, I cannot really plan it in advance. I might want to decide something on the spot without even consulting it with my family. One solution to the problem is using cash or debit cards for all those expenses. This should already help.