Neutral Density Filters
When shooting outdoors on a sunny day, you might be forced to shoot at high shutter speeds. This will give you no, or little, motion blur. Unless you are going for a specific effect, most of the time you DO want motion blur, because this helps to make your footage feel movie-like. Therefore, a ND filter is a nice accessory to have.
My top pick: Aurora-Aperture PowerXND 2000 Variable ND filters. See my full review here.
If you can be next to the camera to adjust the focus, then here is a great manual follow focus system from Lanparte – I use it on all of my cameras
Here is an expensive, but top-of-the line follow focus system for use on gimbals, steadicams, cranes, and in any situations where you can’t directly full focus yourself.
If you are using wireless follow focus, you also want to have a wireless video system, to make sure you are correctly adjusting the focus. Here is a kit from Cinegears that I use