My grocery store (Safeway) offers a strip of coupons with the register receipt. Sometimes the cashiers forget to give the coupons to customers so the strips can get pretty long. I make sure to ask for mine when I pay, and sometimes on my way out I will see if the other registers have coupons that haven't been given out. Every time I ask, the cashier will give them to me.
The coupons are usually valuable, like $2 off next grocery purchase or free merchandise. Today at the store I ended up with 3 free products and $6 off my purchase, all from these coupons.