Scrumptious black-bean veggie burgers with guacamole and salsa may be the most unexpected find at this nostalgic, pink-and-green neon, drive-in ice-cream stand that’s been around for decades. Beefy burgers, sloppy chili dogs, and fresh-cut fries are preludes to creamy, hand-dipped milkshakes, hot-fudge sundaes, and other cool treats.