If all the system needs to really do is connect to the camera and pull down images, then pretty much every modern laptop should be able to do that without breaking a sweat. Simple an inexpensive Intel Core i3 systems can be had for cheap, but do read reviews.
Your key factors are going to mostly be the general size/weight, and battery life. After that you would need to consider data volumes and flow. How much do you need to store at a given time? Would you be recording a small enough volume to easily work with an internal SSD in the 120-250GB range? (For cheaper systems) Or would you need to rely on hard disk drive storage, external, or paying extra for a larger internal SSD?
Something like a MacBook Air may meet your needs and have a very reliable build, or a similar style windows system, but do keep in mind that the aluminum bodies can have issues for field work, namely they get bloody cold in a hurry, and can be more prone to collecting dew than a plastic body.
*Edit:*
Personally I tend to suggest laptops, with a standard version of a mainstream operating system, over Tablets because I find the software is generally more robust and less prone to frustrating errors and annoying quirks. Things like native USB ports, and having multiples, can make work flows easier, and means less bits and pieces to keep track of over carrying an adaptor. However, most tablet solutions will probably cost a little less and be a little lighter, but possibly at the cost of transfer speeds and data storage options.
Lots of give and take in planning out something like this.
Try sitting down and writing out a story about how you would expect a shoot to go. Focus on details of your actions, and you can get a better idea of the solution that can work best for you.
Canon EOS 7D | EF 28 f/1.8 | EF 85 f/1.8 | EF 70-200 f/4L | EF-S 17-55 | Sigma 150-500
Flickr: Real-Luckless