The Collaborative International Dictionary of English v.0.48:

packer \pack"er\ (p[a^]k"[~e]r), n.
   1. A person whose business is to pack things; especially, one
      who packs food for preservation or for the market; as, a
      pork packer.
      [1913 Webster]

   2. A ring of packing or a special device to render gas-tight
      and water-tight the space between the tubing and bore of
      an oil well. [U. S.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

packer
    n 1: a workman employed to pack things into containers [syn:
         packer, bagger, boxer]
    2: a wholesaler in the meat-packing business [syn: meat
       packer, packer]
    3: a hiker who wears a backpack [syn: backpacker, packer]