Go through everything before you put it away for the summer. Throw away, give away, or recycle classroom decorations, posters, bulletin board paper, etc. that you no longer want to use. Keep only one paper copy of each assignment, handout, and test that you think you might use next year. Recycle the rest. Pester students until they've picked up old projects still hanging around your classroom. The more you deal with now, the less you'll have to go through in the fall when you are juggling meetings while trying to get everything ready for a new school year.
Buy a flash drive and download all of your files from your school computer and server. Servers are not infallible and there's nothing worse that arriving in the fall and finding out that everything you left on the server (and its back-up) has disappeared.
Are you one of the lucky teachers who knows exactly what classes you'll be teaching in the fall? Well, now is a great time to make copies of all those handouts you'll need for the first few days of class. At the end of the school year, the copiers are usually line free, unlike those workdays right before school starts!
Not sure what classes you'll be teaching? Look through your files and see if there's anything you can copy ahead of time. For example, many of my first day activities can be used in a variety of classes so even if I'm not sure whether I'll have 2 sections of World History and 1 section of U.S. History or 3 sections of all World History, I can make 3 sets of my first day activities because I know I'll be using 3 sets no matter what.
Pick one school related project you'd like to complete over the summer. That's it. You need to rest, relax, spend time with your family, and do things you enjoy that are not teaching related. You want to come back in the fall re-energized for the new school year, not exhausted and tired.
Put a vacation message on your school email account and voice mail. Resolve to only check them a few times over break.
Now, you are ready to run out of the door and embrace all that summer has to offer!