Stir-fried pork with banana chilies at a Kanchanaburi restaurant
Like many tourist destinations, Kanchanaburi has lots of restaurants to choose from, but nothing particularly special. The 'thing' to do for dinner here is to eat in one of the big floating restaurants that you'll find near the bridge or close to the center of town. Some of these can be detached and towed up and down the river, but these are usually used for groups.
Personally, I avoid the floating restaurants as they are generally poor quality for the price. There are several small, mostly open air, places along Mae Kwai Yai road, which runs along the river. Many of these places serve drinks as well as food.
A particular specialty around Kanchanaburi seems to be a stir-fry using the fragrant Thai basil, called pad cha. Unlike the very common pad krapao, which uses the much spicier holy basil as well as lots of garlic, pad cha is a much milder dish, but one with a really distinctive taste. Be sure to give it a try when you visit Kanchanaburi.