I have just started playing, and am accumulating a whole bunch of junk. Some items are clearly ingredients, some are clearly non-useful, and then there are the ones that I can't tell if they're quest items or something else:

Specifically:
  • Are shells useful for anything? I've tried using them & nothing seems to happen.
  • What about the Zombie Painting? Is it a quest item or useful at all or can I get rid of it?
  • What about guitars, soap & pitchforks?