Can you tweet from a Kindle? Not with its built-in tools. But if you'd like a break from all that serious reading you're doing, bookmark KindleTwit as a Kindle-friendly Twitter interface.
You can post through a simple text input box, read your Twitter stream, and check out your replies. You'll have to write direct messages the old-school way ("d username Hey there ..."), and forget about media previews. But if you're going Kindle-only on a trip, and can't stay away from the blue beast, this looks like a convenient way to indulge.