Just south of town, off US 31 is a mall with Lowes, HD, WalMart, movie theater, and several other stores. On the other side of the highway from there is a Meijer's supermarket. If you have time to explore, head over to Charlevoix. Shopping along the main drag and there is a decent restaurant (The Wren?) at the bridge over the channel to Lake Michigan.
If you haven't already found it, there are a lot of specialty chochkie shops in downtown Petoskey, in the area of the City Park Grill.
Ooops, my bad! That should be US131, not US31.