Even telling your next of kin is no guarantee of getting the funeral which you'll want. When I was a child my mother frequently told me that she wanted to be cremated (as she hated the idea of 'being eaten by worms'). She repeated that information to me many times in adulthood. However she either never mentioned it to my father or he simply decided that he wanted to be buried with her because he arranged her funeral as a burial (with a joint plot).
The best you can do is to tell as many people as possible or, failing that, put it in your will (where it still won't be binding upon on anyone) AND keep a signed (and dated) card in your wallet saying (for example) "In the event of emergency, please contact xxxxxx at yyyyyyy. In the event of my death I give consent for my organs to be used for medical donation and I desire that my funeral be arranged in accordance with the document stored in in the top drawer of the desk in my living room".
Chris