Protecting private key on USB flash drive: how to?

[Faramir]

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Well, I am going to carry gpg in my USB flash drive, either using
portable firefox+FireGPG+some way to put gpg on the drive, or portable
thunderbird+gpg for portable TB+enigmail. But despite what way I will
use, I will be carrying my private key with me... since there is no way
I will protect it with my life (and it is not worth of that), I'd like
to know the suggested way to keep the key safe. I think I will use a
very strong passphrase, but maybe there are other measures that can (or
should) be taken...

 Thanks
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