Could you please help me understand the meaning of a poem by Ivor Gurney, an Englishman who fought in the First World War.

From his "Laventie":

Of Maconachie, Paxton, Tickler, and Gloucester’s Stephens;
Fray Bentos, Spiller and Baker, odds and evens
Of trench food, but the everlasting clean craving
For bread, the pure thing, blessed beyond saving.

I highly appreciate your assistance.