Waterproof Bag

A Waterproof bag is required for NATO participants.

Expect rain, fog and other types of wet weather. You need some moisture protection for your gear.
Not only are these correct for the era they are also very utilitarian. The bag itself is large enough to protect your sleeping bag and pad, plus a change of clothes..
A waterproof bag will fit neatly in the large compartment of your ruck sack, keeping the contents dry when you are forward deployed.
These are easy to get, and are inexpensive.