A lot of data technology is already small and light. Taking in to account one of the precepts of ultralight backpacking,if you can cut your weight, do it. Here's some stuff I found that is small and light.
Media is getting smaller as the capacity increases, and smaller media means smaller readers. Even if your digital device (camera, etc) does not take one of the smaller media forms, like MicroSD, you can get an adaptor for the media to scale it up to fit your device, and use smaller readers to transfer the data.
http://www.engadget.com/2009/05/05/eagletecs-nanosac-microsd-card-reader-makes-mouse-balls-look-bi/
Pull the MicroSD card out of your device. The reader is so small, the media goes in to the USB plug rather than sticking out of the device. What hangs out is essentially the handle that allows you to grip it. Does the library have a no media policy, but an accessible USB slot? Nobody will know it's there because it's so small.
Don't have MicroSD in your device?
http://www.kingston.com/flash/sd_micro_adpt.asp
Like Russian nested dolls, this adaptor takes MicroSD and scales it up to SD form factor so that you can use it in a miniSD or postage stamp-sized SD device.