I am a registered organ donor, I would also like to give blood but have had a transfusion which rules me out for a while.
I am not sure if they would want my bits following my transfusion but they are welcome to them when I die. I doubt I will miss them terribly
Seriously though I think that it is such a great thing to do. I know I often go through life looking at what I have achieved and sometimes it is easy to think well I have done nothing, BUT I know that I will always be able to do something for someone else when I die so makes my life less pointless