Hey, I'm new here. I'm really sorry if this has already been discussed, but I have a flight tomorrow, and need to know some extre precautions to protect my guitar.

The guitar had a cracked headstock. It was repaired and you can barely tell it was ever cracked. I know I should slacken the strings due to some tension thing. What else?
Thanks in advance.
Wrong forum, I'm afraid. This is just for questions about the forums themselves, not guitar stuff. Hate to be "that guy", but you'd have a mod come along and tell you anyway. So as to not be just a pain in the ass, slackening the strings is all that comes to mind. Welcome to the forums
El Gearo:

Fender '69 Reissue Mustang
Fender American Standard P-Bass

Fender Blues Junior
Yes, you should definitely slacken the strings and keep it in a case or a low humidity area any time you leave it alone for a long period of time.

RNR is right though, questions of this nature would be long in the guitar and bass basics or electric guitar forums.