Goose's Gags and Gifts is the name of a chain of novelty shops owned by Goose Gladwell.
Although there is some question about Goose's truthfulness in other areas, Goose is telling the truth about his business. His stores are successful enough that they're known outside of Springfield and its state. When Goose meets Bart, he introduces himself (in a tongue-in-cheek fashion) as having "over 20 stores in over 30 states." When Goose distributes Bart's T-shirts, they become nationally known, appearing on magazine covers and drawing the interest of the Disney corporation (which eventually purchases the line of shirts).
Goose's Gags and Gifts carries what would be considered standard items for novelty/joke shops: Rubber chickens, dribble glasses, Magic 8-Balls, models, comic books, and so on. Other items carried by Goose's store in Springfield include falsies and a rapping toilet seat.