Grand Bend is very much like Sauble Beach and Wasaga, it is a summer party town. The population explodes to about 10x its normal number during the summer. It is mainly summer boutique shopping, bathing suits, gag t-shirts, etc. The best place to park is in the parking lot behind the colonial hotel, near the beer store (on #21, north of the first lights). Easy access, and easy exit. This allows you to walk down the street to the beach.
I like the Pinery Flea Market (Sundays only), about 5 miles South of the Bend. I don't have a preference for food there