If You Want to Do More Than Just the Basics with Your Resignation Letter. You can always write more, and craft a longer resignation letter, but the truth is that it isn't necessary. You can add a portion of the note where you thank your manager or boss for the opportunities and time you have had together, or add that you hope to keep in touch, but in reality, if you really feel this way you probably should make an effort and find an opportunity to say these things in person (rather than getting an email).
Prepare for It. Your best option in this scenario is to accept it with dignity and make sure you're ready to leave the office for good when you turn in your resignation letter, whether that means gathering up your personal items or making sure you've collected the names and contact information for the teammates and clients you'd like to stay in touch with.