Looks like I will be staying the night here as the slow boats don't reach Houay Xai until after the border crossing shuts (deliberately or otherwise).
The settlement of Houay XaiI , sandwiched between the Mekong and a range of hills, is a popular border crossing with Thailand . Thirty-day Thai visas are available on arrival in Chiang Khong on the Thai side.
Once you're across the Mekong and past immigration (daily 8:00-17.30), you can get one of the regular buses to Chiang Rai (2-3hr) or Chiang Mai (5-6hr).
Houay Xai's only real sight is hilltop Wat Chom Khao Manilat , boasting a tall, Shan-style building of picturesquely weathered teakwood, now used as a classroom for novice monks.
Thaveesinh Guesthouse seems to have all the amenities and sells boat and bus tickets. Also worth a look might be Friendship Guesthouse with its rooftop balcony.
The no-frills Mouang Neua restaurant dishes out decent Lao and Chinese meals - the vegetable omelette is good. The lively Nutpop, a few blocks north, does stir-fry dishes to order, cold beer and delicious fruit smoothies, while nearby Ban Midtapab offers excellent fish and views across the Mekong.
The Riverside restaurant is located looking out over the river. The setting is pleasant and they serve traditional Lao dishes as well as the usual fried rice and noodle favourites. Their Sindad, a Lao favourite, a type of soup/grilled meat do it yourself barbecue at the table comes recommended.