I've been doing a lot of unilateral (weight on one side) farmer's walks recently, and all of my clients do farmer's walks in some way at some time. Here are a few resources on this excellent exercise:
Jedd from Diesel Crew on Farmer's Walks
Shon Gross on Farmer's Walks on T-Nation
This post of mine has some tips and a link to Jim Smith's advice on farmer's walks.
Dan John on unilateral farmer's walks
Grab some weights and get carrying.