Call it a picnic with a purpose. On a recent late afternoon at Craig Park in Fullerton, a few dozen people — many of them Fullerton PD officers — gathered under a canopy for food, sodas and water and dessert, followed by an old-fashioned relay race on an obstacle course. Casual visitors to the park might have assumed participants were enjoying a typical picnic on a nice spring afternoon. But the get-together actually was a big thank you from the non-profit Community Service Programs to the FPD for its efforts in combating drivers under the influence of alcohol and/or drugs.…