flagging with a note

It is important to me to flag my emails so that I can return to them easily so I can resolve or check on issues. I would like to be able to make a note on the flagged email as to exactly what needs to be done to the email. I could save them to another file but that wouldn't work since I am not the only one checking these emails and not always on the same computer. Can anyone tell me if I can add a note to a flagged email?