Paper wallets, but really just the private keys.  That look something like this:

5Kb8kLf9zgWQnogidDA76MzPL6TsZZY36hWXMssSzNydYXYB9KF

But can be made to look like this:

5Kb8kL
f9zgWQno
gidDA7
6MzPL6T
sZZY36hWX
MssSzNyd
YXYB9KF

And practice restoring them, to make sure you know what you are doing.