Personally, I like to take the time on tour to get as far away from technology as possible. But if you insist....

I second the Asus eepc + flash drives. Light, cheap, does the job.

If you really want a full-fledged PC, either Macbook Air (if money is no object) or a used 12" Apple Powerbook. The PB is about 4-5 lbs with power adapter, very rugged, has an optical drive, big hard drive.