Problem: Often when going to a grocery store, we get a receipt and almost immediately throw it away. And if we do keep it, it's incredibly difficult to track a specific receipt/line item.
Solution: It'd be great if there was a service that managed our receipts as soon as we made a purchase. For example, when I go to home depot, I would get the option to print a receipt, email my receipt, or upload the receipt to this new service. When I get home, I can then look up any item I've ever purchased or to find a receipt by date/store/city/etc.
Monetization: Charge a monthly subscription or a one-time fee for the service. You can also use the data from the receipts to target ads (since you know where everyone is shopping and what they are buying).