One of my daughter's favorite things to do at the store is to help me play "coupon fairy!”
If we have coupons for products we aren't going to use, we play "I spy" and try and spot someone with those products in their cart, then give them our extra coupons. I have never had someone refuse a coupon, and it always puts a smile on their face (and leaves them with a good impression of couponers!) You can also leave coupons nearby the applicable product (or tape them on so they don't get thrown away), hand a coupon to someone in line behind you, or drop off extras at a coupon swap box.
Note: Avoid leaving any Internet printable coupons. Sadly, there have been stories of KCLs sharing their printables, only to have their recipients make copies of them and use them; then the unsuspecting KCL’s coupon printing account is suspended because of fraud. Also avoid accepting or using any third party printables where the validity of the coupon cannot be established.