Camera specific packs rarely carry well. Look for a regular weekend style (~3000 cu. inches/ 40 50 liters) backpack that will comfortably carry at least 30 lbs.
This is my camera (only) pack. It opens from the back (harness) with a heavy duty zipper, so it is easy to throw it down and work out of it suitcase style, without dirtying the harness. 5X7 (in LowePro Omni Traveler), 3 lenses, Pentax spot, 6 filters, 5 film holders in insulated lunch bag, various sundry items (notebook, glasses, repair) in pockets. The pack also has room for a water bladder, two zip top pockets for day's clothing and lunch, and a large mesh pocket on the back.
And no, you can't have my giraffe.