Thank You, Come Again!
It's no secret that stores survive on repeat business. It's in their best interest to get you coming back -- even if it reduces their mark-up by a smidge (and that's usually all it is). Many stores, both brick-and-mortar and online, offer discounts on future purchases when you buy something, but for some reason they're not always obvious.
These coupons may be on the bottom of your receipt, or they may be in the box an online purchase arrived in, just tossed in there with the packing list and the catalog. So remember to look for these things. A few sellers that commonly use this technique include coffee shops, online clothing stores and drug stores.
Speaking of online ...