Most planes nowadays have a charging port where you can plug in your phone for the duration of the flight. Therefore, I recommend getting an emulator on your phone and playing games on it. Usually if I want something casual, I get an NDS emulator and play Pokemon Platinum or HGSS. Other recommendations are FFIV, Etrian Odyssey III, Shin Megami Tensei, DQ4, some of these are ports but they run well on DS emulator.
My personal experience (US) is that most airplanes have chargers nowadays. However, the charger is very loose, and I could never make my charger fixed in the socket.
If OP could find a good socket, then this lucky person could enjoy 5 hour gaming with no interruption :)
I might be talking out of my arse, but you could bring a toothpick with you and try removing any fluff/grime from the socket before plugging in. Worked for my phone when the usbc charger wasn't secure.
I haven't tried this personally but maybe if you use a short extension cord it would work better? This should remove the weight of the DC adapter pulling on the connection to the outlet