It sounds like your house is not quite level, or the kitchen floor or something. Have you considered using small magnets? You can get the advertising ones about anywhere or buy the flat ones and put one on the cabinet and one inside the drawer to help it stay closed. You might also consider readjusting the tilt of the rollers/tracks to make the drawer slide IN rather than out. A slight tilt would do it. Just a thought. Hope this helps.
Good luck....hope the links help you out.
They sell thin strips of magnetic material with adhesive backing on it. You can cut them to the perfect shape and size needed.
If loosened or poorly angled tracks aren't the problem, try putting the heavier items in the drawer toward the back of the drawer.