You will feel like a Pac Heights local when you squeeze in the door of Jackson Fillmore, one of the liveliest Italian restaurants in San Francisco, serving basic, well-executed fare. The setup is better suited to singles-who are seated at the tiny bar-or three or four people, the magic number to lay claim to one of the densely arranged tables. Couples generally end up at the bar. Gregarious types should have good luck striking up conversations over the free round of bruschetta that starts off the meal. A long-standing local institution, Jackson Fillmore captures the simpatico camaraderie of those who live nearby.