Check your Paypal account. It will show every payment you have made or recieved since you opened it.
Check your Feedback. Scroll down to the bottom of the page and click on Leave Feedback. Any items you have not left FB for will be there. You can also look at Feedback Left For Others for your other purchases.
I record my purchases in the same book I use for my sales. Too old school to trust these electronic gizmos.