[GordonS]

> One thing I really want to be able to do with a blockchain system is to put my wallet in cold storage—like, in a safe

AFAIK, you can generate a paper wallet with any blockchain system. You're keys are rendered as a QR code and/or series of words (there is a name for this protocol that hopefully someone else can remember!), and you can then print and store it.

Hardware wallets are also a thing for some systems, such as Bitcoin.

[mbrock]

Yeah, exactly. BIP39 is a common protocol for mnemonic keys also supporting subkeys. Hardware wallets like the Ledger Nano S have support for Bitcoin, Litecoin, and Ethereum, and they let you sign transactions without ever exposing your private keys to a general purpose computer. And yeah, you can always just keep your private key in any way you want—it's just an n-bit number.