Save all your receipts, install this app, snap a picture of your receipt, submit it, get points, win rewards! You can choose prizes from amazon cards, PayPal, etc. It's useful, easy, and fun.
https://play.google.com/store/apps/details?id=com.infoscout.receipthog&hl=en-Google Play Store
https://itunes.apple.com/us/app/receipt-hog-get-paid-to-shop/id525373618?mt=8-AppStore