Head into an REI and pick out a pack that fits you - carrying 40 lbs, fit and comfort are your biggest priority. Usual drill - load the pack with 40 lbs of weight, and carry it around the store for 15-20 minutes while you're shopping for something else, and see if it fits your frame.

Personally I have settled on the Kelty MAP 3500, available at http://www.amronintl.com/kelty-map-3500-three-day-assault-pack.html. Its about $95 in the non-camo colors, its bomb proof, and carries a load well on my shoulders. I use one as my every day day pack out hiking, which carries gear for an emergency overnight etc. I don't think it meets your criteria for lots of pockets - it has no more pockets than the average pack, and imho no more pockets than are necessary. The MAP has tactical applications (I've seen military deploying with them) but fits in on the trail. I own a few, one has had weekly use for the past 3-4 years and it has held up really well, no tears or stress failures. I bought a couple more and built my office GHB in one, and another bag I keep at home. They fit my back and are familiar and comfortable from the get go, typically holding 25-30 lbs.

Gregory also makes some very nice packs, personally I like the Tarne for about $125.

In the event of a disaster, wearing a back pack will make you stick out no matter what you want. A tactical bag wouldn't really stand out so much more than another bag of similar heft. So you look like you might have bought it from Cabelas, big deal.