Define what is long, and what devices you'll be bringing.
Gaming-worthy laptop? Buy Kerbal Space Program.
Only Android/iOS devices? Download the Kindle app and peruse the free e-books - there's a lot of good ones.
Also, obviously, the Dark Side of the Moon album of Pink Floyd.
I heard Fallout:Shelter was a good Android game.
And if you're not above downloading movies (reminder: downloading music, in most places, is just as bad an offence if you haven't bought it), there's the whole Marvel Cinematic Universe that is amazing.
And if you like/are open to anime, there's quite a few to try out - Paprika, Paranoia Agent, Children who chased lost voices, Patema Inverted, anything by Hayao Miyazaki, Summer Wars, The Girl Who Leapt Through Time.