'pack rat' definitions:

Definition of 'pack rat'

noun

Someone who collects things that have been discarded by others [syn: magpie, scavenger, pack rat]

noun

Any of several bushy-tailed rodents of the genus Neotoma of western North America; hoards food and other objects [syn: packrat, pack rat, trade rat, bushytail woodrat, Neotoma cinerea]

From: GCIDE

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]