Is it risky to use the laptop in the bus?

Especially for the laptop's hard drive, due to all the vibrations while the hard disk is active?

What about putting laptops in rolling backpacks?

You can use laptops while traveling on a bus. However, a huge bump could mess up the platters. They do make shock resistant hard drives now which have definitely saved me in the past. I got a nasty bump on the laptop (ie dropped it while it was booted) and the hard drive immediately realized the shock was beyond the tolerance and shut down. I got a notice on the screen that the drive had taken preventive measures to keep my data safe.

As far as your backpacks go, it would be safe, but I would recommend that you either Shutdown or Hibernate the computer. Do not use sleep mode as it can sometimes keep the disk spinning which is never good for transportation.