Context? Limitations? Number of secret holders? Are both parties verifiable (ie. can you exchange some information beforehand to verify identify?) Is data retention a concern?
Email signed by PGP or a one-time pad. Can the person be trusted with a thumb drive (and to not lose it or have it stolen)?
There's a number of ways with various security levels and I'd say most are "secure enough". For example, I'd trust my friend with a thumb drive that had an encrypted archive on it with a shared passphrase if the archive contained semi-sensitive information. Why? I doubt anyone who finds the lost thumb drive would have the technical knowledge to break into an encrypted archive and a lengthy passphrase would make bruteforce attacks take years on the off-chance they know how and would even try.
Email signed by PGP or a one-time pad. Can the person be trusted with a thumb drive (and to not lose it or have it stolen)?
There's a number of ways with various security levels and I'd say most are "secure enough". For example, I'd trust my friend with a thumb drive that had an encrypted archive on it with a shared passphrase if the archive contained semi-sensitive information. Why? I doubt anyone who finds the lost thumb drive would have the technical knowledge to break into an encrypted archive and a lengthy passphrase would make bruteforce attacks take years on the off-chance they know how and would even try.