After I get visa, ticket, insurance, hotel bookings etc, I scan everything, as individual pdfs.
Two types of documents, one which are crucial for journey, others which are just for help. Then I make two folders on my dropbox, Important and Informative. Visa, flight ticket, hotel booking, insurance, tickets, passport info page etc pdfs go to Important. Travel guides, tours, map, weather info etc go to Informative. Then I merge all pdfs in each folder as a new pdf, print two copies of each on A5 double side. Staple each copy on top left corner.
A5 size makes them smaller enough to store, while keeping them easily readable. Double side printing also cuts the volume in half.
One set of Important goes in luggage, second stays with me in my camera-cum-document bag, along with original passport.
Both booklet copies of Informative pdf stays in luggage. I use one on vacation, second is as backup, just in case.
Originals are only my passport, my national ID, money cards etc.
Edit: I also carry a ziplock or two, almost of A5 size, and I shove all the receipts, bills, tokens etc I get while on vacation in them, and sort it when I am back home.
Edit2: I use FolderSync Android App to keep this folder two-way synced with my phone, and almost all the times airlines hotels etc are ok with a soft copy of the document, as they just need a number to locate my data in their systems.