This large-capacity pack delivers a startling number of bells and whistles for a great price. It also comes with a removable daypack for side jaunts. I also recommend the Patagonia Porter . Like all Patagonia products, the Porter's workmanship is top notch. I particularly like the shoulder strap - you can carry this bag like a suitcase, a backpack, or a duffel bag.
All straps stow away for airplane travel.
I especially advise you to look at the Bora 80 from Arc'teryx . It has a number of features you'll find as handy when traveling as when climbing, such as a large external pocket with a drain, a detachable fanny pack lid, and a full side zipper for accessing the whole inside of the pack. Mountainsmith has long offered some of the best bang for the buck in technical packs. Their Antero is a slimmed down version of that company's venerable Frostfire. At 4,000 cubic inches it will carry most anything you need comfortably for a relative bargain price.