You should monitor his reaction to milk carefully. In nature, only babies drink milk, but adults don't. Milk contains lactose and the body needs to produce a special enzyme to be able to digest that. But most animals only produce this enzyme while they are babies and stop producing it when they grow up. So most mammals (with the exception of some, but not all humans) become lactose intolerant when they grow up.
The signs of lactose intolerance include stomach aches after consuming milk, bloating, producing gas and diarrhea. This can lead to constant discomfort and pain, and the diarrhea can lead to dehydration and malnutrition.
Before commercial dog food was available here where I live, people fed their dogs the leftovers from the kitchen. That includes bread, cooked potatoes, pasta or rice (whatever was available), eggs, leftover vegetables and any meat that was cut off and not for consumption (or let's call it "animal product", because it includes meat, skin, organs, tendons, cartilage and uncooked bones). The dogs basically got everything humans could eat, but didn't eat.
This type of food is not ideal for dogs, though. Too much starchy food like bread, pasta, potatoes or rice can make dogs fat while still causing malnutrition because it lacks vitamins and minerals.
The big problem is spices. Food leftovers usually contain salt and spices, but dogs shouldn't eat them or only eat them in very small quantities. So it would be best to set aside some surplus food for the dog that doesn't get seasoned or to wash off as much spices as possible before feeding leftovers to your dog.