I don’t carry many accessories with me these days but two items that I recommend you keep in your kit are a polarising filter and a neutral density filter (often referred to as An ND filter)
An ND filter, reduces or modifies the intensity of light giving no changes in color. The purpose is to reduce the amount of light entering the lens.
Doing so allows you to select combinations of aperture, and shutter speed that would otherwise produce overexposed pictures.
This is done to achieve effects such as a shallower depth of field or motion blur.
For example, if you wish to photograph a waterfall at a slow shutter speed to create a deliberate motion-blur effect.
To obtain the desired effect, let’s say a shutter speed of 2 seconds was needed. On a very bright day, there might be so much light that even at minimal ISO and a minimal aperture, the two-second shutter speed would let in too much light, and the photo would be overexposed.
In this situation, applying an appropriate neutral-density filter is the equivalent of stopping down one or more additional stops, allowing the slower shutter speed and the desired motion-blur effect.
Whilst a little more expensive my recommendation is to invest in variable type of ND filter as this will provide an unlimited range of density thus allowing you to change the strength of the filter