One of my favorites is RFC 1149 which is entitled A Standard for the Transmission of IP Datagrams on Avian Carriers. Yes, it’s about implementing the internet using carrier pigeons. There have been a couple of attempts to implement it, but I don’t think that any of them have been very successful.
There is digital data being transmitted by carrier pigeon though. Here’s the story of how a white water rafting company gets its pictures of the customers back to the office to be printed and waiting when the customers get back.
My understanding is that this is actually an implementation of that tried and true protocol known as sneakernet, rather than RFC 1149 or one of the IETF blessed standards. Sneakernet may be old and nonstandard, but it still has its place. You continue to see it even in trendy, new fields like cloud computing.