Some ideas…
-Rope climbing or pulling (Makeshift sled pull?)
-Kettle bell work
-Farmer walks
-Deadlifting (barbell work in general)
-A regular pull-up regiment. (I have a set of Metolious "Rock Rings" that get daily use and do a better "roughening" job than a normal pull-up bar. http://www.metoliusclimbing.com/rock_rings.html)