From Grand Theft Wiki
Grand Theft Auto: San Andreas, Grand Theft Auto: Liberty City Stories and Grand Theft Auto IV. It is a spoof of cereal manufacturer Kellogs. The company name can be found on some vans in GTA San Andreas and on a website in GTA IV. Certain cereals include Cok o Pops, Crunch Flakes, RAILS, Dragon Rings, and Popping Cherries. Their motto is "Everybody loves Biglogs in the morning" which is a sexual reference to awaking in the morning with an erection.
The company was founded in 1908.
A Cok 'o' Pops advert inside of a 24/7 shop.