Many stores now offer you cash back or rewards for bringing your reusable bags to their store instead of using plastic bags. Target gives you $0.05 off for each reusable you use for your purchase. At CVS, you can pick up a green tag at the registers (0.50-0.99) and you'll receive $1 in Extra Care Bucks (prints at the end of your receipt and can be used on your next purchase - works just like a gift card) every 4th visit. At Kroger supermarkets (Ralphs in SoCal), you get rewards points on your membership card. At the end of the month, you'll get special coupons mailed to your house.
Now, these rewards aren't significant but the important thing to remember is that you'll be reducing the amount of plastc bags you use. Plus, Los Angeles is very close to banning plastic bags at retail locations. If this new legislation passes, you'll be charged $0.15 per plastic bag - and who wants that? So go out and get yourself some snazzy reusable bags and keep them in the trunk of your car - just in case you stumble upon a good deal :)
P.S. - I almost forgot to mention Starbucks! Take your reusable mug and order a tall size of your drink of choice. They'll fill it up no matter how big it is. So you could get a grande or venti for the price of a tall drink! Plus, they'll give you $0.10 off the price!