In Mice and mystics, Should party items be place in paw to use them?
Those cards aren't counted against your pack limit at all.  You simply place the corresponding token in the party items area (the middle of the clock).  Page 18 states


  Party items are items that can be used freely by any mouse in the
  party. When a mouse receives a party item, place the card near the
  story control board and place any marker or token that might be
  associated with that item in the party stash area of the story control
  board.