A sleeping bag. Make that a sleeping bag with below zero degrees Celsius
comfort temperature.
A bottom sheet.
An inflatable sleeping mattress.
Waders. Breathables, since we will be hiking to some extent.

I just have to ask, why have an inflatable mattress if you are preparing for
cold weather? I went late season elk hunting with about 18" of snow, and
that night one of our hunters got hypothermia because he was sleeping on an
inflatable mattress. The physician in the group had to drive him into
Pendleton. That mattress allowed the cold to penetrate from the side of the
mattress, where those with the old foam standbys were toasty warm.

Just curious.