You can always make a large pack smaller but not vice versa.
30L is a pretty useful size.
Pack the 10 essentials, plus particulars for task and any conveniences you like.
Prefer flat earth-tone colors to keep a pack useful for normal town/school/travel tasks.
The right shade of gray takes on whatever colors are around it and looks "normal."
Prefer non-reflective trim, zipper pulls. I'll add them if I want them, but don't want them printed or sewn in.
No molle, prefer less- to non-mil look.