The 32 oz "Big Gulp" was introduced by 7-11 in 1976 in Southern California:

https://en.wikipedia.org/wiki/Big_Gulp

Even bigger sizes arrived in the 1980s:

Called Big Gulp because it was initially the largest such drink available at any retailer, 7-Eleven eventually introduced larger sizes. In 1986, they introduced the 44-US-fluid-ounce (1,300 ml) Super Big Gulp, followed by the 64-US-fluid-ounce (1,900 ml) Double Gulp in 1989 (later reduced to 50-US-fluid-ounce (1,500 ml))...