Beyond the basic necessities, different folks have different ideas
about what to carry in a survival kit. YMMV

But I agree completely with the idea of being prepared.

One of the most valuable bits of training I ever received was USAF
"survival School." And a fundamental warning was, "never fly over
anything you're not prepared to walk out of." (Of course there are
exceptions, but the concept is sound.)

Throughout many years of flying, I've always had my own collection of
survival items stuffed into the side pocket of my flight bag and never
took off without them.

DaveinFLL