If you do this, you should find out that what you were eying will most probably be a want; and that you will not need it. But, your mind will still think of buying the thing right?
One way to prevent this is to PROCRASTINATE! Hear this, PROCRASTINATE. When you procrastinate on buying the stuff, it is likely that over time, your interest will wane and then you will 移情别恋,although you might say that 移情but did not 别恋. (You know who you are) For example, you procrastinate leaving the house to go to the mall, and maybe a few months later, you will have a new interest. This results in you actually saving a fair bit of money.
Another way is to be contended, 知足常乐. If you are contended, you will never long for other things, and will be happy :D. What you have is really a lot more, even when you are not comparing at those African kids. Look at the low-income people in Singapore, and you should realise that you have much much more than the others. If you have more than others, you should not be asking for more right?
So the final advise is to not splurge, because of some present want, as you might need the money in future.
*PS- I am not practicing what I preached. I am planning to buy something that cost $200+ which is obviously a want, and not a need. =P