check out "receipt pal" and "receipt hog"
Both apps earn points for every receipt you enter and you csn use the points to get giftcards (amazon, etc)
They accept receipts from grocery, any restaurants, any stores, pharmacies, gas stations and gas pumps.
Between the two I've made over $120 in the past year and now I ask for a receipt for everything I purchase so it's good training also. I no longer feel weird asking for a receipt for $1 items and more people are becoming familiar with the apps too. Often I'll snap a pic of the receipt right there on the counter just to make it less suspicious.
Receipt pal also lets you email receipts
Both have extra ways to earn points also