All schools are different, but nothing that was required for either son had a few day turn around. And not much required from the athletics department. Most things were school requirements such as medical forms, placement tests, etc.
One thing to watch out for. Most schools force you to opt out of medical insurance. If you don't your bill will be several thousand more. Assuming your kid is covered, you'll likely want to opt out.
A few things that helped with my oldest, and hopefully with my youngest have been.
1) start using Google calendar (or similar) for everything. Put everything in the calendar. Besides helping with things coming up, it's sometimes very helpful to look back.
2) I've tried to stress to my kids that if you have something that can be done in under 10 minutes....Do it *now* do not procrastinate. I am not holding much hope that this will stick.
3) A bit off topic, but have your kid start using a password manager. The idea being is you do not want to share passwords across websites, etc. At the very least make sure their passwords for college are unique.
4) Have forms for medical and possibly financial power of attorney filled out, and notarized (if necessary) before they go away. Once they turn 18 you will have a difficult time at best dealing with any medical situations if you do not.