You've asked for a way to view your purchases, and now you can! Head to your Personal profile on the web, then click the 'Reports' section. On the left, choose the 'Purchase History' report, and voila! You're now able to see a history of your purchases for each studio you visit, whether the purchase was a cash, credit card, or 'other' purchase (check, free, etc).
See the screenshot below for an example of your new Purchase History!