@carsoffortlangley I’m late to the party and haven’t done much overlanding but have done a good deal of wheeling, backpacking, multi-night canoe expeditions and camping. A lot of what others have already said is great I’ll just add a few things.
Basic cold weather gear, especially at altitude it can get cold fast and you should be prepared
Well stocked first aid kit
Multiple ways to start a fire (lighter, matches, flint, etc)
Hatchet and Saw (either to clear obstacles or prepare firewood)
Shovel
A good camping chair (this is more important than you’d think)
Headlamp
Things like tent, sleeping bag, mat and so on are important but vary depending on where you are and your preferences so I won’t make any recommendations other than to buy quality gear so you don’t have to buy again after a season of use.