I wouldn't run with a pack. More like climb a long flight of stairs while wearing a pack as part of your workout. Running with a pack will eventually give you back and/or knee problems.

I do this for a workout. I climb a very steep, long flight of stairs as fast as I can while wearing ~30-40 lb. pack. Then I run 3.5 miles in hilly country.

I drink at least 4 quarts of water a day and take vitamin supplements and eat a pretty high protien diet. It makes a big difference in the way I perform. If I know I'm going to be in the backcountry for more than a couple days I eat and bring alot of fatty foods and some carbs.