the amazon adder
This article mentioned you can get an "Order Report" from Amazon for physical orders placed (tldr: your Orders page has a "Download Order Reports" link, and then there's a pretty simple interface, the long time reports take a while to generate but they'll email when it's done.)
You get a CSV file you can pull into a spreadsheet program. Or, if like me, you're not particularly adept with spreadsheets, you can open the CSV file in a text editor and then copy and paste the contents of the file here. (NO information will be sent online, everything is happening locally in the browser.)
This page will then crunch the numbers and give you a chart of what you spent per year in each category, and then some tables, sorted by the total spent: by year, by month of year, then by category. The category view can then drill down on an ordered-by-total list of what you bought in that category.
(Disclaimer: this tool is kind of crude code written when I was feeling rather unwell. I made guesses about date format and everything being in one currency, and that the columns are in the same place for different people. And what's missing in the data from Amazon, oddly, is electronic fufillments. I'd love to see what I've invested in my Kindle library, that someohow seems more worthy than most of the gizmos and what not I've ordered. Why Amazon doesn't include that or have an option for it is a mystery.)