Good traditional attire in your answer. But I am thinking it is not "required" nowadays ie the tweed and breeks?

I know some traditional "shoots" still expect the traditional attire, neck tie included. Especially if one expects or hopes to ever be invited back! But isn't that becoming rarer nowadays ie the expectation of traditional dress? I think your mention of a "camo jacket" being fine answers that one.

I know what I would take. And it isn't traditional. If cold enough, a base layer of NZ Icebreaker long underrwear in super fine wool. Then a layer of polarfleece green long sleeved shirt on top. A green or brown polarfleece jumper or zip up jacket. And finally on top my Beretta Coat with waterproof lining. For trousers my Beretta hunting pants. I assume they are three layer and stay dry underneath. Way too heavy for any hunting I have done in Australia. Leather waterproof hunting boots. Heavy wool socks. My feet have stayed dry in these unless I step in a puddle above the top of the boot. Good idea on spare socks though. On my head probably a polarfleece soft cap.

I think all of the above would be too hot for stalking and walking up mountains and hillsides. If so, eject a layer. If it is too much, the polarfleece jacket could go. But as one knows, One gets hot and sweaty walking and climbing. When one stops, if it is cold enough, the sweat quickly cools and chills set in. Then a layer in a backpack becomes handy again.

I have never tried using the knee high breeks. Kiwis used to love their shorts even in very cold weather. I guess they make it easier to walk up hillsides without heavy trousers in the way. And mean the pants legs don't get wet from the tussocks.

Interesting how much it rains in Scotland.