Get them to come back with delight.
Stick a gift or discount coupon on coins. Make it a thin layer of transparent material, so it’s not easily detected when they get their change at the store. Print on it the coupon and sneak such a coin into the others you give them as change. Then watch them come back with delight.
A game to make your customers more involved in shopping.
Print a photo of a part of an item’s packaging, so that if you stick it at the same place as depicted in the photo, you’ll have to take a second look to realize it’s a picture attached to the packaging. On the other side of the photo print a voucher for a gift or a discount coupon. When the customer ones such a “hidden in plain sight” voucher they can take it and use it to get the gift or discount.
To engage the visitor and on the way offer him opportunities to buy, and make sure they have fun and leave with good memories. The last impression before they leave is the most important, so this will help them remember you fondly.
When he enters the store, give him a small card with a good headline selling the first step, something like “You already have a surprise waiting for you. Just find our blue shelf.” There he’ll find the next step, maybe “The surprise is in our best selling book. You have two tries to find it. It’s on this shelf.” Inside the book there is a coupon and further teaser instructions (like: “If you want more on this subject, we have another surprise, go to our games section and look for the clue.”) Don’t only use coupons and discounts, do a raffle, give them a chance to pre-order something, just give them a small gift etc. also tell them they can ask for help from your staff.