[GrumpyYoungMan]

First and foremost, relax and recharge. The hard work will come again soon enough. Go out to a long lunch or have a team lunch or something, for example.

Second, take some time to take care of yourself professionally. Now's a good time to network with former colleagues and other people you haven't talked to in a while, to spend some time learning about something that will enhance your skills or to make sure your résumé is up to date.

Lastly, take some time to clean up your workplace. Take care of old tech debt items, update documentation, and, in general, take care of any part of the systems you work on that have been neglected for a while. There's always something that needs maintenance.