Hiking with your dog can mean more than just grabbing a leash and heading out. It can involve a detailed process of choosing clothing that is functional and perhaps cute too.
When it is cold outside, especially if your dog is short haired, consider getting a overcoat for the dog. There are a variety of options. Some cover only the back. There are others that go all the way around and cover the stomach too. This is especially great when you hike in deep snow. The full jackets such as the Ruff Wear Cloud Chaser helps the dog keep his tummy warm.
On the other hand if it is extremely warm you might consider getting a swamp cooler for the dog. This is a shirt that you soak in water and put on the dog. It helps dissipate the heat but releasing some of the heat as the water in the shirt evaporates, just like a normal swamp cooler.
Boots are another consideration. Many dogs such as mine may hate them with a passion. Some may even be quite good at sneaking them off. However boots can be very valuable. If you are hiking in an area that salts the salt can be quite tough on her paw pads. When it is cold the boots can help keep her warm. Similarly when it is warm the boots can help keep her from burning her paw pads on hot asphalt. Also if you are in rocky area or rough areas they can be quite beneficial to give extra protection.