Id say it depends on how you would use it in general and more specifically as well. Like, what percentage of time would you use it while traveling vs in the office/home office or as a Tablet vs Laptop replacement. That might dictate whether you need travel accessories or not or a docking station or protective casing or presentation aids.
So if someone says my travel case is the best accessory along with extra battery pack and Miracast Adapter etc. that may or may not be useful to you. Some people have specific work flows they try to stick to and want to duplicate as closely as possible and that drives their desire for different accessories. Others adapt their work more to the device.
So for me... and what I do, I try to use native capabilities of each device as much as possible adapting my work style to each device as much as possible. I have a docking station but its not the MS one because I use it with other devices as well, I wouldn't want to be without it. Even so I use my Surface as a tablet more than a laptop/desktop. I probably use the on screen keyboard more than the MS Type Cover and my Full Wireless keyboard docked more also. I have an aversion to Bluetooth devices and avoid them as much as possible ... they are historically bad IMO and this mood predates the Surface.
I already had a decent bag which I use for travel but that's an important thing to have when needed, it's not likely the bag I would have bought if I was starting with the Surface but I'm not replacing it just yet.
I use a Netgear Push2TV 3000 for attaching to any monitor or TV for presentations, works with anything that has an HDMI port, it's small and I know I can rely on it when needed.
If you want that all put together look for appearance's sake at high level meetings you might want a classy folio case.
Ooh, you got one of my early morning ramblings ...
Now to change my clocks and spring forward to... morning. Blackbird has spoken, morning has broken.
