Different situation, but exactly the same prescription as [this answer](https://fitness.stackexchange.com/a/7012/1771). Lift, get bigger, then after you have a basic level of strength, train for your specific task of carrying things.

Take up Starting Strength or another all-around heavy compound lifting program (squats, deadlifts, presses, chin-ups) and supplement with farmer's walks and Atlas stone carries/lifts. The SS [wiki][1] gives you the bare minimum of information in order to take on the program. The 2nd or [3rd edition book][2] is details the program in full.


  [1]: http://startingstrength.wikia.com/wiki/Starting_Strength_Wiki
  [2]: http://www.amazon.com/Starting-Strength-3rd-Mark-Rippetoe/dp/0982522738/ref=sr_1_1?ie=UTF8&qid=1340845725&sr=8-1&keywords=starting%20strength