A couple of ideas about the practicality of lugging around a collection of SD cards.
First instead of full size SD cards; Micro SD. I've got a couple, they're as small as a dime, one of mine is 1gb. They come with a piggyback that fits in any SD slot.
Second, all these cards could be fitted in pouches sown on the reader's carrying travel case.
Third an
SD Jukebox could be created at about the size of a PDA to contain at least 50 plugged micro SD cards.
An other thing missing on the market as far as I know is a wire with a plug that would fit in an SD slot. That would aid to plug an
SD Jukebox to an SD slot.
The market so far was built around the fact that for bigger content the cards you use have to be bigger. But if a quantity of locked cards is a factor, nothing today exists to cater to this need.
And worse WE DON'T GOT DAT D....D READER YET!!!