The rate of personal data accumulation is just crazy

The rate of personal data accumulation is just crazy. Today I discovered I had only 8 G of disk space left on my new MacBook. I have had the MacBook for about 2 months and I was already 93% (112 G/120 G) through it. How can this be? Reviewing what was there I see

8 G free
5 G software development tools/applications (ok this is what I use for a living)
6 G other tools/applications (ok, some of these I use for a living, others for fun)
30 G customer data (ok, important to have and to keep)
23 G personal data (what!)
40 G that I couldn't specifically attribute (what!)

How did this happen? How did I have 23 G of personal data? It turns out that 10 G of it is an iPhone development video lecture series: Once I watch it I can delete it. But still, 13 G was just my shit. And this does not include all the gigabytes of data I have on my home server. 13 G is a lot of personal stuff. Perhaps not any more with the number of images, music, movies, and other large digital formats. But then, I really don't want to store those movies and that music I own. I just want their use whenever I want. But, alas, I can't have that yet without incurring the cost of storing them.

The lesson is that while I can manage some of this growth -- thin out my personal collections every now and then -- I can't manage most of it and so I need to find a really cheep source of local storage. Sigh.