- Data files.
- The Internet.
- Installed apps.
If nothing else, check that you have up-to-date backups. If you have automatic backups setup, don't just assume they're up to the minute.
Your Internet is up and running right after your boot to your desktop? If you use a wired connection through a router chances are you don't need to do anything. But what happens if you're on Wifi? Be sure you know the SSID and security settings.
You'll probably want to check those online accounts to see if you remember their passwords. If you set your browser to remember the passwords for you, this becomes even more critical. You might think you still remember but it's a good idea to check and be sure.
Have your desktop set up just the way you like? Maybe you'll want to export a list of installed apps for later reinstallation. This way you won't forget to install something you need. It's an old trick really but it should still work. The downside is when packages get renamed, things might not work out.
Of course, I always prefer to reinstall as I go. Install an app the first time I need it. This way the system is kept as lean as possible and really old apps I don't ever use don't get reinstalled.