Im not a big fan of the zip-off "daypack," either. One of those things just screams, "Tourist!!!!" I prefer to look around at the locals and adopt whatever they are using for a day-satcheloften some kind of inexpensive shoulder bag. Much better.
But, the daypacks can of course be zipped off and left home. The additional cost of the daypack to the main pack is tiny. Were talking $20.
For the most part, I think a wheeled duffel works fine. In many cases, it's easier to roll a big bag than carry it. It's amazing how much a duffel can hold, and they're pretty easy to manage. REI's Tech Beast ($229) is fantastic. Loads of room (5,900 cubic inches, but with a duffel there ALWAYS is room for one more thing), lots of stash pockets, tough construction, and excellent roll-ability. Very nice. Similar, but smaller, is Eagle Creek's ORV Trunk Wheeled Duffel ($275). With just under 4,000 cubic inches of capacity, it will take some tight packing for two weeks. But that will force you to make good decisions.
An interesting option is Osprey's Meridian Wheeled Duffel ($319). It's the same size as the REI duffel, and has the option of carrying on your back. I think for the most part you'll drag it, but I can see time or two when you'll hoist it up. Keep in mind, however, that it may weight 50 pounds. Easy to hurt yourself.
If you just want to haul a lot of stuff, then go to Patagonia's Freewheeler Max ($400). Massive. 7,500 cubic inches of space. You won't put this on your back, but you sure can pack the freight with it. Good wheels and very tough construction, with separate pockets for shoes and gear.