What is the best, calorie-rich food for birds in cold climates?

I put out bird seed every day and wondered if there is something better suited for birds in severe weather.
In winter, I occasionally mix bacon fat grease and seed to make suet but want to improve on that. Knowing that a Junior Mint is 10 calories and made of mostly sugar, chocolate and corn syrup, would that be a good addition?

We are entering the month of January in Western NY. Often the temperature here will never get above freezing for the entire month. It is -5C right now. The birds in the area are a mix of: blue jays, cardinals, chickadees, pine siskin, mourning doves, etc. As I type this, I can see chickadees flying down to the feeder, and returning to the nearby tree to eat a seed. The energy expended in this cold weather must be tremendous. Every year there are die-offs due to this poor energy trade.
Ignoring the cost (Junior Mint are many times more expensive than shelled sunflower seeds) would a few Junior Mints mixed into the food for the larger birds be helpful?
I usually put out ~1 kg, 2 pounds, of seed a day. Would 100 grams of JM be a healthy addition?
I am hoping a biologist/nutritionist can tell me if this would help or hurt.