I use an Osprey Variant 52 for my overnight pack. Good for hut trips as well as a few days of camping and carrying a tent. Maybe I could get away with a little smaller, but there would not be much point, as trying to cram everything into too small of a pack just results in a poor carry.
Not sure how folks get away with minuscule sized packs, perhaps in really temperate regions, or for spring only… Around here I want a good, solid, real tent, as winter nights are long (and often windy), and there is way too much hanging out going on to be comfortable in a bivy or with a tarp. Same with a bag, I need a real bag. If the weather report is really good/warm, I’ll take my 15 degree Marmot Helium, but usually I have to bring the 0 degree bag to be comfortable in winter. If you have enough free time, enough energy, and a deep snowpack, you can forgo the tent and dig a really good cave, but plan at least a few hours to pull this off. I am not a fan of vapor barrier liners/socks, but I do use generous amounts of foot powder, and my liners dry in the bag at night. I always carry extra socks, but no additional clothes other than a big puffy and booties for around camp. Keep boot shells in the tent when sleeping, otherwise they can freeze your feet in the AM.
Sometimes I need a rope and a little gear as well. Add the big puffy, food, fuel, stove, some camp booties, an extra pair of socks, and the the usual day gear, and the 52 gets pretty full.
This pack is pretty light, and compresses down nicely with the top pocket removed for riding during the day out of base camp. Avoid the temptation to buy too small a pack, especially if you have inclination for technical descents or terrain where you might want to carry some climbing gear.
Of course, if you are at altitude in somewhere like AK in April, you will need a little more…

Edit: The above refers to my typical approach, of touring in to a base camp, and then doing day riding around the camp. I like to be relatively comfortable at basecamp, and then travel light and fast during the day. As Kyle notes above, his approach for a traverse is a lot different, which makes sense since he is always carrying all of his gear on those trips. For a traverse like that, packing like a single push alpinist makes more sense.

Pretty keen for some input on my gear list. This would be for a 3 night tour camping at between 3500 – 4000m with nigh time temps between -20 and -35 degrees celsius.

One set of merino thermals for day
One set for sleeping in
Micro down jacket for touring with
Warm down for around camp
3L jacket and Bib pants
2 pairs of gloves plus merino liners
Headtorch
Alpkit Zhota 3 person mountain tent (split between 3)
Mountain equipment Everest bag with silk liner
Thermarest neoair x-therm
Primus omnilite Ti
1.5L fuel bottle
Snowpeak Trek 900
Spork
Micro towel
Small Medi kit with thermal blanket
2 Nalgene 1L water bottles
15L Snowpulse Pro rider in addition to Pack for all other gear

Interested to see what suggestions are on Boots for Camp. Options are either Sorel Caribous with wool liner to wear in sleeping bag or use Snowboard boots moving around camp and take in some Rab expedition down booties?

Any other suggestions of where i could cut weight some things i should add etc.

I’ve got a North Face Catalyst Micro down. Theres a coating on the down to help it withstand moisture that seems to have worked so far plus its slightly longer in length than most offerings from other companies.

I guess I’ll take both my Sorels and some booties on the trip and depending on the distance into base camp will weigh up if its worth it. I’ll need my sorels on the trip regardless.

Another option would be to remove snowboard boot liner when returning to camp and replace with the wool sorel liner leaving the sorel shells back in town…?