When I’m hiking in the Highlands there are three things I always take with me and for me it’s a must (beside my Canon EOS 5D MKIV camera – lenses and the Mavic 2 pro drone.)

1. My yellow rescue whistle.
2. The Swiss knife with my name graved into it. (A gift from a dear friend of mine and a great photographer Mr. Marc Imfeld and his wife Barbara Imfeld).
3. KASE Wolverine 100 x 150 filters and the Soft Pouch which holds:
   ND 8 – 64 and ND1000.
   GND Soft Edge 0,6 – 0,9 – 1,2 – and 1,5.
   Reverse GND 0,9 – 1,2.
   Center GND 1,2.

   My filters are must as the light is constantly changing. What I was using for 5 minutes ago is not the same I’m using this minute.
   The Reverse filters are great when the light is starting to come and then you change to the Graduates when the light is higher in the sky and so on.
   Then you can mix them together like using the ND and the Graduate filter and so on.

Well for me they are a MUST like the water (which I also carry with me).
I also have some other first aid kits if something goes wrong.