With about 40yrs of camping behind me I've accrued 'stuff'. BUT, a bunch is spares/extras that just sit at home for a 'rainy' day.
I have a checklist that I've refined over the decades that contains things that I actually need or have needed. The checklist is what I pack the vehicle from and so it all fits and since I pack the same way I can at least find things as needed without having to unpack the entire vehicle
That said, it is quite amazing what can fit in the back of a mwb vehicle if you have a decent rack as well.
I have slowly scaled to more compact stuff, modern tent, modern sleeping bags, inflatable pillow, thermarest pad etc. Ditto for clothes that suit the weather without being stupid bulky. I find that you can save considerable volume by choosing the above wisely.
cheers,
george.