I think your idea is fine. One may also use compact flash cards - I occasionally tote data to and from work using a CF card from my digital camera - I have multiple card readers at work and at home. Similarly, either directly or indirectly, one may use SD/MMC cards (my Palm Pilot uses them and I also have a couple of readers for that format card)

As for water - fret not about fresh water. If it gets immersed, dry it out and use it. Salt water, OTOH... if there is power to the device, that would be bad. If your jump drive gets dunked in salt water, flush it out VERY well with fresh water (tap is OK) and dry it out before use. If you're really paranoid, follow a tap water flush with a final rinse of distilled water. I have NEVER had a solid-state disaster from freshwater dunks and in fact regularly use fresh water flushes on electronics that need cleaning up. I've even had the interesting experience a few times of seeing electronics gear accidentally immersed and continuing to run under water - fresh water, mind you!

If you're anticipating being around the ocean, I'd look for a water-proof container like a tiny Nalgene accessory bottle or something like that.

Bottom line is that I would be a more concerned about accidental zapping from static electricity (and that does not worry me) than I would be about inadvertent wetting or immersion. Water's just not that big of a deal.

Regards,

Tom