A small head torch with spare batteries. Either Halogen or strong LED's are the best.
Any personal medication and a small first aid kit to deal with common problems such as blisters, sunburn or insect bites.
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.