With the current price of memory cards, I will just bring more cards, no moving parts and sometimes can even survive being cleaned in the washing machine. Not forgetting small, light and don't need batteries.
Ah. This makes sense. And this is, in my humble opinion, one of the main reasons why one would choose to have a portable hard disk device to directly transfer your photos from the cards to the HDD as a backup copy.
If you already have the iPad, perhaps you can consider the iPad Camera Connection Kit. Allows you to transfer your photos from your SD card or camera. Cost $38, cheaper than another harddisk. Supports jpg and raw. But of course that's assuming you have you iPad with you when you travel or on the move.
There are many on the market but are usually slower in transfer. The two I can think of that are pretty much cited by many photog are Nexto and Hyperdrive. Else bring along a smaller laptop along with a usb portable harddisk to connect. Can surf net as well