Depends on the type of hike, if its for a whole day, I pack water bottles, bag of kibble, portable bowl, float toy in case we come across a clean lake, spare leash just in case, etc.
Today it was only about a 5 mile hike, and since it wasnt hot, I left the water in the car and he carried couple cans of dog food in each pocket and my keys and cellphone.
But dont worry, it was not cold at all, around 50 degrees

I usually dont put a coat on him unless it gets below 30 which hasnt happened yet living in NC.