It sounds like your using a Camera Body with a Single CF Slot ??
So my advice would be similar to others in that you should look at what a normal days Imaging is going too be, then get 2 Cards. I'de suggest a minimum of 2 x 32GB Sandisk CF Cards.
You might then look down the track at getting a Camera Body that has built in back up, i.e.. 2 Cards, I can't imagine going on a trip to say Africa with a Camera that has only a single Memory Card.
Unlike some, I've had a couple of bad experiences with CF Cards, in particular Lexar 128GB Cards, I purchased 4 of these about 18 Months ago, had one dead on arrival, another corrupted after a full days shoot in Botswana, around 1500 Images on the Lexar lost (I did eventually save about 70% of the Images with "San Disk Rescue Pro", a great piece of software.
What that experience taught me was to always set up my Cameras so I have both Cards saving at the same time (so I have 2 copies of everything I shoot, hence the requirement in my case for 2 x 128GB Cards), this is fine on the 1Dx as they are both CF Cards, the 5DMK III you run intro the issue of the Canon Software built in bottle neck of the SD Card, ridiculous software limitation still not fixed by Canon (Nikon doesn't have this issue where they use a mix of CF/SD Cards) on the 5DMK III the write speed of the Cards is governed by the speed of the SD card & Canon's limitation on SD write speed.
Another heads up on Memory Cards is the recent release of OSX 10.9 Mavericks, I have 3 Card readers, the Sandisk CF Card reader (works fine still), the Lexar HR1 Hub Reader (reads up to 4 cards at once in a stacked hub) works fine still, and an older Lexar Card reader that reads a CF card & SD card in a pop up head, this reader no longer works under OSX 10.9.
I hope this helps, my experience with Lexar CF Cards doesn't appear to be widespread, but I no longer buy Lexar Cards, I stick now to 128GB Sandisk CF & SD Cards.