The Jargon File (version 4.4.7, 29 Dec 2003):

gorp
 /gorp/, n.

    [CMU: perhaps from the canonical hiker's food, Good Old Raisins and
    Peanuts] Another metasyntactic variable, like foo and bar.


The Free On-line Dictionary of Computing (30 December 2018):

gorp

   /gorp/ (CMU, perhaps from the canonical hiker's food, Good Old
   Raisins and Peanuts) Another metasyntactic variable, like
   foo and bar.