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I know, every answer is as close as your phone screen or (please no) "Alexa!" but there is something wonderful about reference BOOKS. You know? The kind that work when the internet is down. The kind that will come in handy in a zombie apocalypse. (You can look up first aid in a print encyclopedia, and then bash a zombie in the head with an unabridged print dictionary...)
Indulge in a complete set of encyclopedias:
You can pay big bucks for for new ones here. (World Book is still publishing sets.)
You can get great deals on old ones here (Mine are from 1998, complete with giant dictionaries and a reference guide. It's kinda great that they don't include 9/11 or social media, but will totally be there for me in the aforementioned zombie apocalypse. )
You might get lucky with old ones here, too.
And of course, this is the ultimate online encyclopedia right here. (Wiki WHO?)
The Britannica iPhone and iPad apps are great, too -- but try not to spend too much time staring at your devices!
Remaining print versions of it are expensive, but worth it.
You can also find some remaining DVD-rom encyclopedias here.
Below, you'll find the reference books I love most from my home library: