Some general tips:
--have a plan to provide liquid water. Some people use heated water dishes, some people carry fresh water several times a day (depending on temperature). At some temperatures, replacing the water in the morning is all it takes to be fine for the day. If you are carrying fresh water, you can save bother by using warm water. It will last longer than cold water before it freezes (but don't use hot, because you don't want to burn the chickens!)
--make sure the chickens have a place to roost without wind or snow getting on them. Chicken feathers are very good at keeping them warm, as long as they are not wet or sitting in a wind. So they need a roof and at least a few walls to protect the roosting area.
--make sure the chickens have enough ventilation. People sometimes try to keep chickens warm by closing the coop up tight, but this can cause new problems (respiratory issues and humidity are two of the main ones. Chickens put out large amounts of moisture in their droppings and their breath.)
--make sure they have enough food. Chickens do not need special or different foods in cold weather, but they do need the ability to eat more. You don't want them to get fat, but you don't want them going hungry either. Most chickens will self-regulate properly when they have constant access to a complete chicken feed. Double-check the water situation too, because thirsty chickens will not eat dry food.
--If you want to provide a treat, I suggest normal chicken food with water added, so it makes a warm mash. Chickens seem to love it, especially on a cold morning when they woke up to find their water frozen (it gives them food and water and a treat all at once! And it makes the person feel good too, watching the chickens enjoy their breakfast

) Using chicken food is easier than doing something like oatmeal (no cooking involved), and is also healthier for the chickens. There is no real danger of them overeating wet chicken food; they will just adjust how much dry food they eat, to get the right total amount in the course of the day.