Excellent! Sounds like you have some good adventures coming up. And I think we can find a pack for you.
Sounds like you might not want to mess with a travel pack, although Ill suggest one or two a few paragraphs down. A good-quality compact backpack might be more in order, something tough and affordable. Maybe something like a Macpac Tekapo 35+ ($130; macpac.co.nz), from a New Zealand maker of excellent outdoor gear. Macpacs stuff is tough and cleanly designed, which I think is just the ticket for a no-frills guy like you. The Tekapo holds about 2,500 cubic inches, which from the sounds of it is about right for you. Its enough for a few changes of clothes, camera, notebook, water bottle, a snack or two.
Granite Gear is another company that makes tough, well-priced stuff. That companys Precipice ($155; granitegear.com) is just a little larger than the Tekapo, but still compact at 2,800 cubic inches. It has a nice, simple design built for function and durability more than for snappy looks. Its suspension is good, too, in case the pack gets a little heavy.
Purpose-built travel packs offer some advantages, such as the ability to neatly stow straps and so on out of the way when checking luggage, should you need to do so. Im with you on the detachable-daypack part; they mark you as an obvious tourist.
That said, Ospreys Porter 65 ($129; ospreypacks.com) is roomy but not huge (3,900 cubic inches of capacity), very simple in design, and rugged. Its really just a tough gear bag with a good suspension attached, no more. Straps stow away if need be, and integral grab handles give you another way to lug the thing around. Its a nice pack.
Have a great trip!