Maconachie was a tinned stew named after the company which made it; T G Tickler was a Lincolnshire company who made tins of jam and marmalade, Fray Bentos was and is a brand of tinned ("corned" or "bully") beef named after the Uruguayan town where it was originally produced; Spillers and Baker's was a big, British milling company originally from Bridgewater but then with a large mill in Cardiff which is now luxury flats.
All those names were industrial food producers, I can't find any reference to Paxton's or Stephens (although Gurney was once a chorister in Gloucester cathedral) but from the context it would seem that they were large suppliers of tinned or otherwise preserved and packed food to the army.
I suppose that there may be a connection to Spillers dog biscuits and Baker's Complete tinned dog food but I don't really know!