I used to bring tons of stuff movies, music, etc. But, somehow I went 180 and now I go minimal. My approach is:
1) I bring my nice in-ear monitors and plug into the IFE system. Even if the movies are crap, I don't really care that much. I have watched plenty of crap movies!
2) I have my kindle with me and at least 2 books that actually want to read.
That's pretty much it. The kindle is pretty reliable, so if the IFE is out I can just read. I'm not sure if this is a 'reduced expectations' approach but my stress level is way down with nothing much to carry and no worries about whether the entertainment will be good!