I'm always surprised how much I forget what works, although I now tend to take clear photos of what I have in each bag from different times of the year, a simple visual reminder of a packing list.
I used to take notes of what I used, what I didn't use, what I would have liked to have etc etc.
Handy to dial in stuff, but again, you have this experience from hiking.
Theres always some improvising with different time of year or specific regions countries, but I've found most of the core stuff remains the same year to year.

Oh, and you can always try certain bags or racks, and if you aren't crazy them, it's pretty easy to resell stuff. I've bought used frame bags and stuff before.