This is a question that may be country dependent, but I would want:
a list of meets that have been attended in the past and coach impressions of the meet (well run or not, stays on schedule or not, how was the judging comparatively)
A list of strengths/weaknesses of the current coaching staff (if new HC is an outsider)
A list or chart of the path each gymnast is on
-for higher level gymnasts, skills they have, skills they are working, and skills they are drilling for
Any needed information (team usag login info, when coaches need to re-certify and redo their background checks, exact duties as HC since these duties vary by gym, etc).
If there is anything unusual about ANYTHING (in our old building, a coach needed to be there 30 minutes before anyone else was supposed to be there to turn the lights on because it took 15 minutes for the lights to warm up to full power). Our current building, lights in the cafeteria (where we do awards for meets) are on a timer. One time, the meet ran late and the lights cut out. At the time, we were new to the building and HC hadn't been shown where to turn them back on, so we finished awards (only 1 age group left) in the dark. The announcer used the light of his phone to read the placements. It would have helped to know where the timer box was.