Bubblegum is a minor gag in the later years of Peanuts comic strips. The gag often show how Lucy blows bubblegum in response to other characters' words. In many of those storylines, Lucy's bubblegum even helps her float for a limited time.
The first appearance of this gag is in the comic strip from December 15, 1977. When Schroeder refuses Lucy to take her out for dinner and believes that it is "a bubble gum chew", Lucy responds by blowing bubbly gum.
The second appearance is in the comic strips from August 3, 1981. Lucy blows a baseball-like bubblegum to his baseball manager, Charlie Brown, and then shows that if she was on a soccer team she could blow a soccer-like one. On the 16th of the same month, she blows such big and light bubblegum that she floats upside down in the air and attracts other baseball players' attention when Charlie Brown is trying to improve the team's concentration at games. This strip was then adapted in the beginning scene of It's an Adventure, Charlie Brown.
In the storyline that begins on March 12, 1984, Lucy is again floated by her bubblegum on a windy day. Charlie Brown and Schroeder are not very surprised and worried by this scene, though. Lucy was blown over the fence by the wind and floated in the outfield. Finally, the bubblegum bursts and Lucy falls down on her back. After seeing it, Charlie Brown thinks he has such a strange team.
This gag would continue to appear until February 1, 1987.