Two slices of homemade sourdough bread smeared with ancho chile mayo and pickled red onions accompany the pork tenderloin sandwich ($8.50) at Picnic (1928 Bissonnet, 713-524-0201). These ingredients go perfectly with the house-roasted pork loin, which is both tender and tasty, with the occasional flavor of caramelized skin. The boxed-lunch…