Where Do You Draw The Line?

I'm Tammy and I have an art material.... issue. I love art materials. I love paper. And paint. And pens. And markers. And journals. And washi tape. But I cannot use all of the materials that I think would be cool to have. 

I deal with art material overload by choosing materials that I know I will use often or can be used in a bunch of different ways. I focus on core art materials {paint, paper, brushes, pencils, mediums}. Kinda like using source data instead of wikipedia. For example, I'm open to buying another half pan of watercolor paint because (a) it expands the color choices for my existing set, and (b) watercolors are open-ended in potential uses. But I wouldn't buy a stencil of a building because (a) it's of limited use. But I say focus because I'm not immune to impulse purchases.

The discussion question for today is...

How do you develop a sane art materials purchase strategy? With all of stuff available for the artist, where do you draw the line {pun intended} between what you buy and what you resist? And what is your weakness, something that you see as a splurge, but you don't regret. For me that might be washi tape. For others, that might be fabric or pens.

Where do you draw the line? Or is there no line?