I dread having to use a client-issued laptop. I've traveled with two for significant periods of time, and it's just a major p.i.t.a. My projects are usually large enough that we work with client's IT staf to review our standard image, virus protection, software policies, etc., and get an exemption to plug into their networks.
All of our practitioners can now get aircards, so this is a bit of a moot issue now. Avoid getting into using client email, use an agent to auto-forward, or use a web interface, and there's not much of a need anymore.