Food is rich in diversity in Thailand. And Thai cuisine is among the best in the world. At any corner in Thailand one finds a restaurant. Many of them are small, simple and cheap. That does not mean, that the quality would be bad or worse compared to an expensive restaurant, recommended by the travel guides. Here you find a variety of restaurants, from the simplest places to some with recommendation and status.
By the way: Most of these places are also good to have a drink in the evening.
If you are hungry after arriving in Chiang Khong on the bus, or you intend to leave Chiang Khong on the bus and you have still time and hunger, than it's a good idea to go to the Fresh Market Restaurant. There you get good food for little money.
When walking the river promenade in the southern direction, following the later small asphalt road to the very end, there are two of these very charming laid-back Thai restaurants. The very last one is Baan Pung Rim Khong. They offer good food, a cosy, friendly atmosphere and a nice view over the river.
Definitely one of the coolest places to go in Chiang Khong is the Houseboat Restaurant. It's a stonethrow north of the border crossing. It's really Thai / Laotion style and it has a big advantage expecially at hot days: There is always a cool breeze on the Mekong.
A stonethrow before Pung Rim Khong is Khum Wang, another Thai Style Restaurant on the river banks.
Another nice place to go for food or a drink is Baanmai Shynaam. The staff is nice and friendly, the prices moderate. Asians and Western Tourists go there.