I know this is an old thread but I am about to embark on this same mission. I will be bringing a portion of my husband's ashes down in carryon. They will be in a TSA approved black plastic box which will likely be scanned in security in the San Diego airport. Flying straight to EIS through Miami so I doubt that my carryon will be scanned or checked upon arrival at EIS. Just going through immigration. I will not declare anything

If you read the government website there are forms and documentation required. It says to come into the office and they 'might' have approval ready in 2 days to return to the office to pick up. It says the only 'approved' place to dispose ashes are 5 miles south of Norman Island. I am hoping that they have no way to know what is coming in my carryon (since it was scanned in San Diego), no way to know where I am going and no way to know what I'm throwing off a boat or dinghy in some remote area in the islands.