You might look at the Freecom Mobile Drive CLS hard drives and get all nostalgic for tapes and other old analogue media.
But the drives themselves are absolutely standard: bus-powered through their USB connection, and capable of a decent, respectable 28MB/sec write and 35MB/sec read for large contiguous files.
They are coated in velvety rubber and come in chunky translucent plastic boxes which are not only great for protection during transport, but also hold a handy index card – and a short USB cable so you can connect the drives wherever you go.
The drives themselves have a little slip of card along the edge, protected by a plastic fascia, that you can write on – handy, since hard disks are now sufficiently cheap that it's not out of the question to keep several drives for different areas of your life, even if you're using your Mac for fun rather than work. (Indeed, the drives' cases stack and lock together beautifully.)
Using hard disks with a standard mini USB interface is smarter than a cartridge system like the old Zip disks, as you don't need hardware to load them; USB is likely to hang around for a while, and the disk mechanisms ought to be robust enough to be reliable medium-term storage.
You can buy a cheap powered dock on which to mount three of the drives at once through a single USB port.
But if you add a drive with one or more already docked, it unmounts all drives before mounting the new ones, which causes OS X to complain.
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