Meat. Cheese. Lettuce. Tomato. Bun. Sometimes simple is better. For 43 years, Sam’s has been hooking up North Beach burger fundamentalists with their midnight fix. Depending on the flow of the evening, Sam’s stays open ’til 3 a.m. Anthony Bourdain stopped by the joint a few months back, calling it “one of the top three” burgers in the world. He might be right.