When you receive a lot of email, it's not uncommon for a purchase receipt or order confirmation to get lost in the clutter. This simple Gmail search string uses the hidden 'receipts' smart label to show you all of your purchases in one view.
To use it, just search for:
in Gmail. The results that come back should be all order confirmations, receipts, and invoices. The search is actually powered by Gmail's Smart Labels Labs experiment, but you don't have to have it turned on in Labs to make use of the search term. It picked up a few false positives for me, mostly from stores that use the same email address for both promotional emails and order confirmations, but that aside it worked like a charm.
We've mentioned how useful Smart Labels are before, and how they work so if you don't have them enabled, head into the Labs section of Gmail and enable them (or just click here). If they're not there for you (they weren't available for me), you can still use this search term to automatically filter receipts to their own label to keep your inbox tidy.
Find Gmail Receipts [Google Operating System]