Green’s Dictionary of Slang

1. (US) any form of canned meat.

1940		‘Heres Some Light on Camp Lingo’ in Phila. Post 28 Nov. n.p.: Dog Food – Emergency rations, to be eaten ‘only after you’ve starved to death,’ cynics insist.
1969		G. Sidney Love of Dying 37: Meat and beans, meat and noodles, corned beef hash. Couldn’t eat ’em. Dog food [HDAS].

2. any food considered disgusting.

1972

(con. 1950s) Jacobs & Casey Grease I ii: Get outta here with that dog food.