"I use an external hard drive specifically designed for this, a Wolverine. It has a cardreader slot built in to the drive, and it is free standing so you don't need to be hooked up to a computer to do it. Just plug the CF card into the slot, turn the wolverine on (rechargable battery operated so no need for AC connection), and your files are backed up with a few clicks. Then when you get home attach the wolverine to the computer and transfer files over as needed.
For most nondedicated external hard drives you need a computer attached to make it all happen."