This is by no means a comprehensive list of things to take but a short list of things that can make a real difference in the comfort and enjoyment of your expedition that you might not ordinarily think of taking.
Camp shower
Although it might be nice to have a shower at base camp when you are off the mountain, I have a different purpose for the camp shower, because it's black it absorbs heat making it perfect for melting snow during the day, fill it full of ice and hang it in the front of the vestibule of the tent and within a few hours you should have litres of water saving time and fuel melting snow. You can also use a black garbage bag for this purpose.
Umbrella
Seems like an odd thing to take but it is actually really good. Low down in places like the Karakoram it's really hot and is great portable shade and in other areas like the lower altitude areas in Nepal, it's great for afternoon rain showers as it's too hot for raincoats to work as they don't wick moisture out when the temperatures are so warm and humid.
Flints
These are very simple and unbreakable which is why I always carry a few of them, one with the stove and one on yourself. Matches and cigarette lighters won't work once they are wet but the flint never fails.
3 pairs of shoes
Sounds like a lot but it's actually a really nice thing to have. Firstly, I do most if not all the trekking in a pair of running shoes all the way to Basecamp, take a pair that you would run an ultra in . Running shoes are light breathable and comfortable. Then a pair of crocs for around camp and in the evening. When it's hot they let your feet breathe and dry out and similarly can be worn with warm socks when it's cold. One pair of gore-tex leather boots for hiking through moraine until you put your mountain boots on.
500ml nalgene
Can be used as a hot water bottle at night and will be my cup while on the mountain.
Two Ultra-light Thermos
The nights are long in the Himalayas so you need to store your water in a thermos or it will be frozen by the morning. Also there is nothing more unappealing than cold water when you are already cold.
Titanium long-handle spoon
Plastic spoons always break and the long handle is perfect for eating dehydrated meals out of bags without getting food all over your hands from the side of the bag.
Inflatable pillow
Sounds extravagant and it kind of is but generally above basecamp I’ll be sleeping in a shared quilt and wearing all my clothes to sleep which doesn’t leave much stuff to use as a pillow. Plus a good night's sleep without a sore neck is priceless.
40 below super gaiters
These go over your boots and add warmth, I’ll be using them for multiple reasons, one is it saves me from having to buy a specific 8000m boot, I don’t plan on climbing 8000m peaks all the time and realistically I will only be over 8000m for one day of the whole trip the rest of the time I will be acclimating at 6000-7000m and 8000m boots are just unnecessary. I have La Sportiva G2 sm I think it’s only a matter of time before we see this system being sold by boot manufacturers where you can buy a boot that is lighter and climbs really well for 6000m-7000m peaks then can add a supergaiter for 8000m. I think systems like this have already been used by Ueli Steck, Killian Jornet and David Goettler.
Superlight synthetic booties/socks
These are my own home made ones that I describe in this post
Airtrim sport mask
Designed to be worn in cold or low-humidity environments to help prevent the dry cough that people often experience at high altitudes, usually leading to a respiratory infection and can end your expedition.
Pee bottle
Very important, nothing worse than having to get out of the tent multiple times a night, get a good quality one you don’t want any leaks, the silicone ones seem to do better in the cold than the Nalgene canteens that crack in the cold. Also a wide mouth is very handy. Ladies might consider a she-wee or I know that my wife has gone straight into a zip-lock bag, that is also a superlight weight option.
Ascent plates
A lot of high-altitude climbs are big snow plods and you can't always wait for conditions to be perfect, so some ascent plates at least for the leader braking trail could be the difference between making it and not. very simple things that clamp on between your boots and crampons and work on terrain that's too steep for snowshoes. Originally designed by/for skiers that needed something to help them get up steep couloirs.
Things I'm not taking
An inflatable air mattress can pop and take up too much space in a small tent and also creates cold spots when using a quilt. A z-lite and back pad from the Macpac Pursuit is enough.
Camelback style hydration systems - the tube freezes in the cold and if used when trekking gets covered in filth/poo and dirt often being the suspect cause of Gastro illness.
