As Google blurs the line between the web, your email and Google Now, more and more of your personal information can be shown in general Google searches (though only visible to you, of course). You can run a query for recent purchases to show up confirmation emails, for example, and the new feature includes a number of useful filtering options.
All you need to do is make sure you're logged into your Google Account and then run a search for
my purchases. Assuming all of the purchase confirmation emails have been funneled into your Gmail inbox (and they probably have) you'll see a list of recent results appear on screen. Click on any of the entries to see more details, such as how much you spent on the item and when the purchase went through.
There are filters you can add to the search too. Try adding a month or year to the search query, or just an extra keyword, like "tablet" or something similar. If you've over-indulged with the Black Friday and Cyber Monday spending, then Google can help you keep track. It's all powered by the automatic purchases label in Gmail.
Hat tip to the always excellent Google Operating System blog for the tip.