You want to carry as less as possible and don't want to take many CF cards with you. So your looking for a 1,8" hdd and a powered usb hub to add to an R-Pi.
But 1,8"hdd cost more and can store less data than 2,5" hdd can.
And because your going to use a powered usb hub, that should give enough power for both the R-Pi and an 2,5" hdd. And its size matters together the hub and R-Pi would be more then big enough to take the 2,5" instead of an 1,8".
Its not that you would save all that much space with an 1,8".
Taking a look at prizes and size for 1,8" you would end up with a 64GB SSD for about €100
(it looks like there arnt new hdd @ 1,8")
Prize and size for 2,5" also for about €100 1TB.
Less than 64GB isnt worth it since 32GB CF cards cost about €40 true its a rather slow card.
So the advice from me would be take a 2,5" hdd and a USB to SATA adapter
i have a comparable device just take out the front with the usb and build the hdd to a self made R-Pi case with the usb hub.
mabey some thing like this beagle box http://www.familie-kall.de/cgi.....?BeagleBox
Oh and about the CF reader
this combines the hub with a CF/multi reader
This one doesn't come with a power adapter but looking at it i see that the option is there