A backpack should be a sturdy bag to hold your stuff, with a suitable suspension system, and just enough straps and/or exterior accoutrements to not impede efficiency.
Efficiency in the backcountry has more to do with knowledge and experience than equipment, which makes the question simple: how little exterior stuff on your pack can you get away with?
The math here is basic: fewer accoutrements make for a lighter pack. There’s only so much to be done saving weight with frame and harness components, and sacrificing function here is short sighted. A 60-70 liter pack will use a bit less than a yard of fabric for the body and bottom, so only ounces can be cut going lighter here, and often at the expense of longevity.
Above is the bag I used on the recent Grand Canyon trip. You can see a good photo in use here. The relatively clean exterior was driven by time constraints more than anything, as I realized that this pack wasn’t going to be quite big enough, nor carry ~40 pounds as well as the Paradox suspension.
The above bag is 1000D cordura, with a double 500D cordura bottom. Two compression straps on each side, and bottom straps (mainly to keep the frame seated. Provision for a top strap, but I rarely used one. Weight as taken on the trip was 20 ounces, not bad for a bag with a continuous 37″ circumference, and functional 36″ height.
I took mental notes on the shortcomings, as I always do. One set of compression straps were mandatory to hold poles when not in use. A front pocket would have been nice, to hold ropes and extra clothes more securely. The roll top strap needed to be 1″ rather than 3/4″, as it got yarded on a lot when passing packs. Some form of upper organization would have been nice, either in a lid or pocket, as opening the bag to get maps and the like got old. Side pockets are not so big a deal in the desert, when you’re using a water bag with hose anyway, and they tend to get torn up.
The above panel went into a pack the same size as the canyon bag, but in different materials and with more features. The body is VX-42, and the pockets a combination of 1000D cordura and a lighter 400D ripstop. 1″ webbing for all compression straps and the daisy chains not shown. The idea here was a pack which would be durable enough for another Grand Canyon trip, waterproof enough for spring trips here in Montana, and enough load control for hunting.
The cost of these features? 12 ounces more than the previous bag, for 32 ounces total. VX-42 is 8.5 oz/yard, 1000D is 10.8. Features make the difference.
They also make building it take a lot, lot longer. Experience makes me confident that I’ll use all the stuff I put on it, but compared to the nice, clean canyon bag, the weight and complexity bum me out. Nothing comes without cost.