The attached PFD file shows the official park Service Picnic Areas. These generally tend to be dirty, dusty and overused, the best places to go are off the beaten path. In Yosemite Valley pack up your picnic and head on down to the river and find your own private beach. In Tuolumne Meadows hike out to the meadow or stop anywhere along Tenaya Lake. Campfires and open BBQ's are not allowed outside the official picnic areas.