I used to read a mystery novel or two or else a long non-fiction book during the long flights to Asia that I took before the age of seat-back screens.
If the book was interesting, it kept me from being bored. If it wasn't, I fell asleep.
Problem solved.
However, I took a flight from LHR to ORD right after the terrorism scare in 2006, so we were allowed ONE item to take on board. I couldn't fit both my laptop and a book into the bag I had, so I spent the first half of the flight organizing travel photos. (No way was I going to check my laptop.) Then I read the inflight magazine. Then I watched a movie I wasn't really interested in but which seemed like the least of a bad lot.
Without a book, the flight seemed a lot longer than some of those 12-hour flights to Japan.