Is this just for storage? For most jobs, I take enough compact flash cards for the entire trip -- they are cheap enough now to do this.
If you bring a small laptop, you can download to the internal or an external drive. If you want to be really paranoid, er, careful, bring two external hard drives and copy your cards to both drives, then keep them separate. One in your bag in the car, and one in your pocket, for example. For this use, even a cheap netbook will work just fine.
Of course, if you need to edit photos, you'll need a real laptop.