What does the constitution say about reserved powers

It depends on what you are talking about. In the ninth amendment the Bill of Rights says that the power is reserved to the people. In the tenth amendment it says the power is reserved to the states. If you are talking about limited government that means that the government can't do anything that the Constitution doesn't say.

That no one branch of the government could have all power and that it must be spread in the Legislative, Executive, and Judicial branch.