This was the some of the kit used by four members of the UOTC during a couple of days on a field exercise in December.
I'm told that these bergens are used to carry "stuff" - food, clothes, sleeping bag etc - from one place to another. A smaller day sack is used for the essential "stuff" for one day - waterproofs, warm kit and that day's food and drink. Small, and still essential, "stuff" is carried in webbing pouches.
UOTC is University Officer Training Corps, a branch of the Territorial Army.