I am currently working as the sole system administrator for a medium sized company and I will soon leave this company for another job.

Currently it looks like that they won't be able to find a suitable replacement before I leave and I assume that I won't meet my successor to show and explain our IT landscape personally.

There is a lot of documentation available, but it's quite verbose and I can imagine that it is hard for someone new to find specific information without a lot of reading. I would therefore like to provide an extra set of documents to my successor that contains the most important things to help get him/her started quickly and smoothly.

Given you would be my successor, what information would help you most to find your way around as the new system administrator? What would be the most important things to have at hand when there is nobody around to ask?