Take a look at the bottom of your receipt next time you check out anywhere. Often there are invitations to complete surveys which can result in anything from a discount on your next purchase (Old Navy does this) to a free item (like the receipt below) or an entry into a sweepstakes (TJ Maxx does this).
Filling out these surveys takes about 5 minutes but the rewards can add up pretty quickly! So make sure you don't throw away your receipts; take a look first before you toss them out (if you're not saving them).
Also, make sure you take a look around in the store when you're shopping or checking out; you can find some great promotions listed on signs or stacked in the form of tear-off pads at the register. The promotion featured below is from Subway (on Alps Road for those in Athens); when you buy a meal this week they will give you an Easter egg with a coupon inside! Mine is for a free English muffin.
On the left is the coupon I received at Subway for purchasing a meal, and on the right is a receipt completed after taking a survey for Subway; next time I eat there I can get a free cookie with my purchase. (Don't try to copy the coupon code; it only works at the location I made that purchase at.)