I would have multiple notes. Looonnnggg notes.
To my husband I would tell him how much I love him, and what I think is so amazing about him.
To the people who have hurt me, who I feel there was a really stupid miscommunication that was never resolved, I would make a final attempt to tell them what I think went wrong between us. Tell them positives things I continue to think and tell others about them, and do my best to let them know even though we fought, I never thought of them in black and white terms, and I hope as they go forward in life they stop thinking so black and white. There are only two people I can really think of who get this type of letter from me.
To my closest, dearest, girlfriends I would tell them how happy they have made me and how much I love them. Maybe write some of my favorite memories, amny of which are funny.
To my parents, I would tell them I am sorry for the loss they are about to endure, and thank them for all they have taught me, most importantly being a good person, caring for others, and being responsible.
To my sister I am not sure. She was the most, or equal to the most important person in my life for many many years. Now, in the last few years we are not very close, things fell apart. It is still surprising to me.