Sangkhlaburi is a small town, and as such eating and drinking options are limited. There is however some very authentic and tasty Thai, Burmese, Mon and Karen food to be found.
For cheap local food, try the decent selection of stands around the market at all times of day while a night market springs up here in the evenings. The cheap beer and tasty boat noodles draw a large crowd of Thai tourists most nights. Of particular note is the wide selection of dessert stands -- it's a great place for a banana roti or some pumpkin custard. The street south of the market also has a few hole-in-the-wall restaurants, though none have English menus.
To see what authentic Mon food is like, stop into one of the hole-in-the-wall shops directly after the wooden bridge in the Mon village. There are no English menus but most of the dishes are pre-prepared and displayed so all you'll need to do is point, and the shopkeepers are very friendly. We tried a Mon-style khanom jin (thin rice noodles with a fish curry sauce and a lot of fresh veggies) and a roasted chicken and garlic with rice dish called kaeng hang lay. Both were a highlight of the trip and cost only 30 baht each.
Back in the town centre, don't miss the extensive Thai and Karen food menu at See Daeng restaurant (in the hotel of the same name). We tried several dishes, including an excellent Karen-style spicy pork salad with savoury pig intestine (no really, it's good if you can manage the texture) and sawtooth coriander rather than mint. A red curry with prawns and a special type of mushroom called hed khon, which grows only in higher climates and is a delicacy in Thailand, was also out of this world. See Daeng is open from early morning until 21:30 and they also serve Western breakfasts.
You're spoiled for choice if it's a meal with a view you're after. Burmese Inn, Phonpailin Resort and Sangkalia River Hut (by the lake on Route 232) all serve up well regarded Thai and Burmese dishes to go with spectacular views over the lake. If you prefer a mountain view, head up to Somchai Coffee.
Speaking of coffee, Sangkhlaburi is home to some regional producers and overall the quality is excellent. Rai Khun Ying is one such producer, and you can sample their outstanding arabica in a small cafe across from the market on Thetsaban 2 in the town centre. Coffee Berry is another fine choice on Samprasob Road towards the wooden bridge. And Graph Cafe on Si Suwan Khiri Road near much of the accommodation has a stylish, jazzy-artsy atmosphere to go with free WiFi, excellent coffee, smoothies and even a few cocktails. They also serve pizza, though it was nothing to write home about. Our only complaint is that the staff at Graph seemed more interested in lounging with their laptops than serving customers.
Also don't miss Baan Unrak Bakery, located midway down Si Suwan Khiri Road. They offer a counter full of delicious brownies and cakes, and serve lunch and dinner. The menu features Thai staples like red curry, and more inventive dishes like potato with cashew nuts and kaffir lime leaves. Their huge fresh fruit shakes are the perfect treat to relieve the midday heat. Baan Unrak also has a large shop featuring woven goods made by local women, with proceeds going to support the Baan Unrak local orphanage and animal care centre.
Another good traveller-oriented option is Blue Rock restaurant on Si Suwan Khiri Road, but a bit closer to town. They offer a range of Thai food and also a few Western standards to go with a laidback, reggae-inspired atmosphere. They also serve beer and cocktails, making it a fine place to chat with other travellers in the evenings. Finally, if you want a more "proper" bar for kicking back, tiny Ban Job across from Graph Cafe offers a range of liquor, wine and beer. It really is small -- only six stools around a one-bartender operation, but its intimate setting makes it a fun spot to meet other travellers and expats who volunteer or work for the NGOs in the area.