1. Queue up tasks that don’t require internet.
2. Buy internet if you can afford it. It’s usually around $10 USD for a full flight.
3. For take off and landing, when they tell you to put away your large devices, queue up audio/e-books for that period of time.
4. For longer flights queue up a movie or else you’ll be at the mercy of the airline. Sometimes, you can’t focus and need a break and I find a movie helps in those situations.
For what it’s worth, I’m incapable of sleeping on flights at all. I would probably sleep if I could and I were lacking sleep.