[zetsurin]

I never had your problem, so this might not work well for you, but maybe it will:

Write everything you spend money on down in a single place before you buy it. If you buy a book and pen to do this they can be your first entry.

Creating an awareness of what you spend money on gives you a chance to ask if you will value the thing as much as your impulses are telling you.

This goes generally, lots of self help people suggest keeping a diary, and reviewing it.