In reply to Cappa:
Pavement slapping with a bergan on is a sure way to destroy your knees, I'd lean more towards either long hill drags or short hill reps. Don't underestimate running in boots either. Once you have a base of stamina, tabbing is largely about recovering enough on the flat to get you up the next hill.
For weight, anything that can be ditched makes sense (bottles of water/sand), as do gym weights wrapped in duct tape. Old fleeces, sleeping bags etc will stop everything shifting around. Maybe a scrap of rollmat down the back. Cinch everything as tight as you can.
Just to 3rd/4th what has been said already however, if you're running with weight, you'd do just as well running harder without. As long as you know your bergan and boots will be comfortable, I wouldn't overdo it.