It may be that you're offering your dog a large variety of foods, which could encourage him to refuse his regular food in order to see what will be offered next. Some dogs are eager to eat a particular pet food for several days, and then suddenly this eagerness vanishes and they eat reluctantly or refuse to eat for a few days. Sometimes this refusal is the dog's attempt to control calorie intake. Overeating can cause a dog, like a human, to experience an uncomfortable feeling. It can be normal for a dog to attempt to relieve his discomfort by not eating or eating very little of his food.
If your dog isn’t normally picky about his food and you've avoided creating "problem eater" habits, a trip to your veterinarian may be in order. Any deviation from his normal habits may be a sign of illness.