Survival is paramount in any adrenaline driven adventure!
To be stranded in the dark is could be fatal therefore one of the items in survival equipment is a strong torch, preferably a military one.
It would be excellent Ideally it should be able to be clipped onto a belt or a pocket.
A water bottle is another item that is vitally necessary, these can be bought in all sorts of sizes with very handy clip on features.
A whistle is a survival tool that may easily be overlooked but it is vital to have on hand to get attention and help if a search party is out looking for you.
A military knife is another handy and necessary tool as is a compass for direction.
In the extreme cold weather or in snowy condition a thermal blanket can be very much appreciated.
A basic medical pouch or kit is essential for those grazes or cuts that can hamper progress if not plastered or attended to.