Burning excess fat and losing weight all comes down to burning extra calories anytime you get a chance.
It's even better if you can do it without much extra effort. While shopping, why not park your car furthest away from the entrance? It will save you the aggravation of looking for a spot near the entrance, and the extra walking will burn off calories that you wouldn't have burned off otherwise. Sure, it's only a few more calories, but multiply that by your shopping trips and long term, it can add up to a few extra pound off that waistline.