I would tend to agree with what Pete wrote but if you're simply wanting some personal recommendations, I've got 2 Camelbak "BFM" rucksacks. Both in desert camo. I use one as a Ham radio bag when I do volunteer work and the other is a dedicated first aid/trauma bag that I use on remote locations while working.

Hard to beat in quality for the price, I got em both off of ebay brand new from private sellers for around $100 each.

They come with a very nice hydration bag/hose system. Might be a little large at 2500 cubic inches/ 42 liters of capacity for a carry on bag.