There is at least one good Mexican restaurant in Chelan, but I can't think of the name of it. Around here, there are so many Mexican restaurants that the bad ones go out of business quickly. LatteDa is great for salads and sandwiches. Bamboo Shoot is a new Asian restaurant, but I haven't gone yet. The locals seem to like it. BJ McDonald's serves decent food. As you drive Highway 2 to Chelan, be sure to stop at Anjou Bakery, just south of Cashmere. Have fun!
Was up there last summer (specifically to review a restaurant) . Results: bad, bad, and even worse!
One thing I will recommend is Cisco's in Entiat, about 20 minutes out of Chelan.
Other than that, have a picnic, there's a good grocery store in town, good fruit stands around town.