The Granite Gear Nimbus Core is one of the more unique packs on the market, as it was specifically designed to comfortably carry bear canisters.
You simply drop a loaded canister in the center of the pack (or "core"), strap it down, place the sleeping bag above it, and you're set. This arrangement has the added benefit of keeping the heavy canister near the center of your back for balance.
Two parallel pockets running the length of each side of the pack hold the rest of your goods. I fit all the gear necessary for four late-summer days in the northwestern corner of Glacier NP, although there was not much room to spare.
There's no lid or lid pocket, but the front stretch pocket is good for holding quick-access items like sunscreen, lightweight shells, or other sundries.
The suspension and proprietary Advection back padding combined for all-day comfort on 18 mile days through Glacier NP. The back panel contoured nicely to my back and breathed surprisingly well, even during extended and exposed uphill climbs.
The pack only comes in two heights, but there are a bevy of holes to allow for adjustment. Tall guys beware: I'm 6'0", and I had to use the top set of holes on the longest torso size to get the perfect fit.
The girthy hipbelt required zero break-in (no bruised hips on day one), and it comfortably bore the brunt of my 40-pound pack.
Without a doubt, this setup is the most comfortable I have ever used to carry a bear canister. The combination of a low center of gravity, easy food access, and a comfortable suspension makes for an impressively effective backcountry rig.