5. Get an aisle seat and walk around every hour or so. Stay away from the booze and drink lots of water. If you bring a water bottle, the crew will often refill it for you.
6. Shut the window shade and turn out your overhead light if you are not using it. You may not notice the light, but the people sitting behind you trying to watch their movies or sleep sure do.
7. Long stopovers are hell, so do some research on the airport in which you will be spending time. Download the airport app, find out where the free Wi-Fi is,and look at traveller tips and reviews. Recharge your devices on the plane if you can, because power outlets are often scarce in airport terminals.
8. If you travel reasonably often, airline loungemembership is something else you will not regret.
Otherwise, if you have a long stopover, check out the lounge day-pass fee. When you factor in what you would usually spend on food and beverages, it can make the fee seem more reasonable.