These are sometimes called sleeping bag liners or travel sheets. More and more huts are stating these are obligatory. It goes without saying that it needs to be as light as possible. So, silk is the only sensible option. Try to get one that is box-shaped as opposed to mummy-shaped, otherwise you’ll end up having an even worse night’s sleep and end up in the morning trussed up, well, like a mummy.
Possibly the most important bit of kit on the list. Spare no expense: get the best money can buy. Have a look at Quies—they specialize in keeping people asleep.
Depends on you? A flannel and a small bit of soap could be an idea. Plus maybe a mini deodorant + toothbrush (no family sized pack of tooth paste). There is no or very little running water in the mountain huts. All the water has to be melted from snow and purchased. Consequently, there is virtually no opportunity to wash. So, don’t consider carrying a real towel, shower gel, razors etc. It is for this reason that the inclusion of “Wet Ones” in your kit are recommended. They have been known to take on a form of currency between group members.
Make sure it’s light, in both senses.
All the mountain huts we’ll use have “hut clogs”; it is therefore not necessary to carry an extra pair of shoes.