Our car was full of camping things. There was hardly any room it it.
Explanation:
Both sentences concern the car. The first one gives us the information that there were lost of things inside the car. The second one completes the thought by saying there wasn't much room in the car, due to the amount of things inside it. To end the sentence properly, without repeating the noun "car", we must choose an appropriate pronoun to substitute it. In this case, there is no better option than the pronoun "it", since "car" is an object.
