Tricky question.

Firstly, I'd imagine it would be close to impossible to know if it's a 9/11-style, 'crash into a building,' hijacker or a egypt air 'I just want to meet my wife again' hijacker. The former necessitates far greater personal action/risk-taking than the latter.

Personally I would probably just do nothing other than login to the plane's wi-fi, buy internet access, and send "this might be goodbye" messages to all my loved ones.