Meaning of "selling war surplus groceries" in historical text

[askingquestion]

I know that surplus is extra.

What is the meaning of it in the text below:
Jack Cohen realized in 1919 that he could profits from selling war surplus groceries and, in fact, Cohen started from a stall in East End of London. Tesco as a brand did not appear until 1924, when Cohen bought from T.E. Stockwell a shipment of tea, which was its first own-brand product.

From the document (in section 2 after the title "HISTORY OF TESCO PLT":
https://accid.org/wp-content/uploads/2019/04/Case-Tesco-PLCformatv.pdf

 

[Mark44]

"War surplus groceries" would be non-perishable items that were used to feed the British soldiers during WW I. I suppose this would include various canned foods or things like dried beans and such.

 

[e_jane]

World War I created shortages. Britain began rationing in 1918. Rationing often results in (or indeed requires) that supplies be set aside for possible future demand. Thus the surplus in food supplies, where said surplus resulted from rationing caused by the Great War.