The right tool for the job...
For short tours, like last weekends 4 day tour of the Marin and Sonoma County coast, I use my road bike with a seatpost rack. bike + seatpost rack + goretex bivy tent + thermarest + down bag = 25 lbs.
For typical touring, like Ireland, Baja California, Colorado, Pacific Coast, Canada, I use a Trek 520.
For expedition touring, like a month long tour in southern Chile and Argentina, I use a mountain bike (not shown).