Mukdahan's night market is the most buzzing place in town for evening food. It has all the Thai and Isan classics, but it's the Vietnamese vendors that set it apart. A few sell băhn dah (they'll tell you it's 'Vietnamese pizza'), which combines soft noodles, pork, spring onions and an optional egg served on a crispy cracker.
There are lots of takeaway treats (barbecued skewers, grilled fish, servings of fresh fruit), but many stalls serving soups, noodles and the like also lay out small tables and stools so you can enjoy a no-frills al-fresco meal.