packrat \packrat\, pack rat \pack rat\n.
   1. Any of several bushy-tailed rodents of the genus {Neotoma}
      of western North America, especially {Neotoma cinerea},
      which hoard food and other objects in their nests.

   Syn: trade rat, bushytail woodrat, {Neotoma cinerea}.
        [WordNet 1.5]

   2. A person who habitually saves items, even those unlikely
      to be useful. [Informal]
      [PJC]