This is the one me and all four of my family members currently use, on every single trip. I have literally traveled the world with this. The girls in both the family pictures, all wearing this backpack. They have men and women versions, same volume.
https://www.rei.com/product/227956/rei-co-op-trail-40-pack-mens
My wife and I are both geologists, we have been "travelling light" for last 35 years :)