You do, cause it's you're body.
If you're dead, it may say you're an organ donor on your license or something. However, if you gave no prior consent, either your parents (if single) or your spouse give the final authority.
Many states have made a person's organ donation intentions IRREVOCABLE. That means a loved one cannot refuse to allow it to happen. So if you put donation on a Living Will or your driver's license, the State will have the only right -- and that is to follow those wishes. If a person has made no declaration of wishes, the decision is with the immediate next of kin. If one person is designated to make medical decisions, that person can override other family members. It used to be that the spouse and children needed to agree, but organ donation is in such high demand that this need for agreement may not be required anymore.
The final authority over what? The answer to this question depends on the subject under discussion.
Who had the final authority over the colonists, royal governors, colonial legislatures, citizens themselves, the English monarch
your family
It was the final act that abolished slavery,and said that congress had final authority over states.
IRS
The Supreme Law of the Land Is the Constitution. And the Constitution has all the laws In it so it has overall authority.
Creon exerts authority over Oedipus.
National sovereignty
For most military matters, Congress has the final say. The president does have executive order over some things, and there are certain ways that the president can get around the power of congress in some matters.
Any time you make a donation to a credited organization you can receive a tax credit one the donation is over twenty dollars. You just need to ask for it when making you donation
Paternalistic
There are plasma donation centers all over the United States. There are a number of websites which have to locations of plasma donation centers in your area. Some of these are CSL Plasma Donation, Donating Plasma and Plasma Protein Therapeutics Association.