I just have a spreadsheet of the itinerary (with important dates like flights clearly marked), with just the name of each hotel, which site I booked it at, the price and if it is already been paid, if any meals are included, and most importantly: Until when I can cancel it for free. Besides that, I just make PDF's of all reservations and other important stuff, and put those in my Dropbox. Those will have all the information I need, even offline. I used to also actually print the most important stuff, but stopped doing so for my most recent trips.
I’m a little bit older and I always print a copy of that document.
I just have a spreadsheet of the itinerary (with important dates like flights clearly marked), with just the name of each hotel, which site I booked it at, the price and if it is already been paid, if any meals are included, and most importantly: Until when I can cancel it for free. Besides that, I just make PDF's of all reservations and other important stuff, and put those in my Dropbox. Those will have all the information I need, even offline. I used to also actually print the most important stuff, but stopped doing so for my most recent trips.