Food, including fun food
Rain protection of some kind if there is a chance of it.
Warm coat for stops, if cold is likely
Navigation, map and compas
Water/treatment depending on availability on the trail.
hat/sunscreen (put on, not carried)
Trekking poles if you use them
Maybe also some fun stuff like camera, smart phone with bird or wildflower apps., gps, binocular or monocular, some archaic trinket or gear to be a conversation piece with the other people or whatever.