Megan McArdle suggests looking back at your history of Amazon.com orders to see what your first order was. (ht)
I was living in Portland at the time, and so, of course, we had Powell's, which sufficed for most book needs. Thus I started relatively late and almost all of my purchases for the first few years were gifts for other people. But I did make a few purchases for myself. My very first purchase was on January 17, 1999; it was Hyman and Walsh's Philosophy in the Middle Ages: The Christian, Islamic, and Jewish Traditions and was for the medieval philosophy class I was taking. My first purchases for myself in the strict and proper sense were a couple of weeks later, on February 1:
Summa Theologiae: A Concise Translation
(Thomas Aquinas; Timothy McDermott, ed.)
Anselm of Canterbury: Major Works (Oxford World Classics)
Despite the subject matter, they weren't for my medieval philosophy class, but just out of interest. The next purchase for myself was on March 13, and was George MacDonald's Phantastes, and then I didn't order anything for myself again until August of 2001, and only sporadically after that. It's only in the past two or three years that I've used Amazon.com very much.