Large rock specimens, another reason for a large pack or pack frame.

base weight only counts if you are going on a trip where you will only carry exactly whats on the list. Of course as OM says, the camera, steaks, smores, camp chair, etc etc still add up and another way of looking at it is "TRAILHEAD WEIGHT". HOW MUCH ARE YOU CARRYING PAST THE TRAIL HEAD INCLUDING A REASONABLE AMOUNT OF WATER? We assume the pack will get lighter than that as you eat food and consume items, and then you may also accumulate some items, like garbage, so that there is a "LEAVING WEIGHT". THEN THERE IS THE AVERAGE OF THE GOING IN WEIGHT AND THE COMING OUT WEIGHT. That is a much more telling number than "living room spread sheet base weight. Hey do you add the weight of a wet tent? Probably not. To me whats important is the change in the actual weight carried over the trip and whether I am going uphill with the least weight, which generally means hiking down into a canyon from a ridge.
Jim