A pair of goggles are essential for Scotland’s winter. Make sure that the vents are covered up with foam or they will just fill up with spindrift.
A head torch with spare batteries that illuminates the mountain. Either Halogen or strong LED's are the best.
Any personal medication and a small first aid kit to deal with common problems or existing health issues.
A cheap orange plastic emergency bivouac bag which can live in the bottom of your rucksack.
A little whistle for attracting attention and weights nothing - the majority of Deuter
rucksacks have one build into the chest strap.