A will does not have to include funeral, burial, or corporeal directions. However, it is not uncommon that people want to include these directions. Even with incredible detail. The challenge of including these provisions is that the will may not be discovered until after the funeral is over, and the body is laid to rest. None of the directions are followed because no one was aware of their demands until it is too late.
So the obvious remedy to this potential situation is to share the details of the funeral and burial directions with those who will be involved with carrying out their demands. Whether by sharing the entire contents of the will with those involved (if there is nothing else in the will that you would not want them to know), creating a codicil to your will with these directions and sharing the contents of the codicil with those involved, or at least leaving separate written or oral directions with these individuals informing them of these provisions in your will, these individuals should be aware of your wishes so they may be performed in case the will cannot be found.
So if you want your son to speak at your funeral you need to let him know that. If you want your body to be cremated and spread over the Atlantic ocean you may want the executor of your estate to know. Etc.
Image by: Burns Library Boston College