Here’s a budget rule: Do not buy things in airports. Unless it is 100% essential for survival. (Gifts for mother in laws etc do fall under this category). A couple of things:
Duty Free: There is something about a duty free stores that makes normal, rational human beings turn into rabid over consumers, buying everything in site because it is marginally cheaper. I understand the odd gift or perfume or electronic device, but for the love of god, you do not need a giant plastic m&m man filled with 10 000 m&ms. (besides, those m&m men are creepy)
Anything Else: Airports are overpriced and you probably only want things because you are bored and they are yelling BUY ME.
Obviously I broke this rule immediately upon entering Ataturk Airport. What I didn’t realise is that if you pay in dollars, they give you change in Turkish Lira, so I effectively lost $10 like that.