[DISC] How do you guys read manga on a flight with no net?

Do you download manga and store them? I'm looking for a way to download multiple volumes but don't from where to do it. I mainly use that app mangania to read manga on my phone and occasionally download chapters. But in case of situations where you won't have net for extended durations, what do you guys do? Downloading multiple chapters one by one seems like an inefficient method to read manga on a plane.

Any sources to download direct volumes from? In high quality?