As a frequent traveler, I know this one thing to be true above all overs: ABC. That's "always be charging." You can't count on having in-seat power. And if your phone or other device dies, so does your lifeline for in-flight entertainment, rideshare arrangements on landing, updating loved ones on your ETA, and so much more. So I always travel with a backup power bank for my phone (and make sure the backup is juiced up, too).
Medicines
Loss and delay of checked-in bags is a notorious problem in this era of chaotic air travel. That's why you must always keep your prescription medicines with you in the airplane cabin, and never leave their whereabouts up to chance by storing them in a checked bag. (Losing your favorite swimsuit, say, is inconvenient, but it's not a matter of life or death, like going without a potentially life-saving medication.)
