Question to those who have a Nook/Kindle/Etc

I'm thinking about getting one for school.  I would much rather DL my text book then have to drag it all over. I'm pretty sure I can do that with my teachers- just need to double check with school.  I'm not though this semester and this would be for fall, so I'm not planning on purchasing anytime soon

My question- can you lock some material so no one can read without a password?  Say I was to let someone in my class borrow my e-reader for a few minutes and they were digging around in it.  I would not want them to find my fic.  I currently have a cheap e-reader that does not lock entries.  

Thanks