Buy suitable mix from soil dealer and dump on top of existing soil, probably with walls around to keep in place. Something with benches on top allows sitting while working.

G. Schenk, COMPLETE SHADE GARDENER (Houghton Mifflin, 1984):

"For partly shaded ground I especially recommend beets, sweet cicely, cucumbers, turnips, leaf lettuce, Chinese peapods, comfrey, kale, radishes, scallions, shallots, chives, leeks, broccoli, cress, watercress, carrots, sweet potatoes[!], spinach, zucchini, cabbage, mustard, and French sorrel. As a rule, leafy vegetables accept more shade than do seed vegetables such as corn, pole beans, and peas, which will tolerate only about three hours of shade daily without noticeable impairment."

See his Chapter 15, EDIBLES (page 256) for full discussion.

For the berries, I would suggest Vaccinium ovatum (evergreen huckleberry), it can handel a fair amount of shade, it's native, and it's a beautiful shrub.