In local Cambodian restaurants, especially the ones in the provinces, the cost of rice is included with the dishes. Technically, it is free. It is also common practice to serve a selection of canned and bottled sodas or juices along with your meals. They are not free, nor are you required to partake of any of them. But if you do, then you will have to pay for it. I have almost always managed to resist getting a can or a bottle for myself. I am just content with the house tea, that vaguely smells like jasmine, that also comes free with the meal.