Depends on the role I'm playing.

To function purely as a DBA, I don't need anything more than SSMS. In fact, for years I thumbed my nose at any third-party tools, simply because I didn't want to become dependent on something that hides the details behind a pretty wizard. I wanted to know how to run a backup using T-SQL, or how to make DDL changes to a giant table using T-SQL, or.... Wizards are nice, but if you don't understand what they're really doing, what do you do when the wizard fails?

To function as a DBA/blogger/presenter/writer/general-computer-user, well, the list is different. SSMS obviously, but I also install, by default, Notepad++, Evernote, Dropbox, Chrome, Greenshot, Ditto, and Zoomit. Can I function without these? Yes, but they certainly make life easier.

A good chair is a plus as well, although I do a lot of work standing up, or on my treadmill desk, or even parked in a recliner. If I could get a standing desk at work, I'd rarely sit down.