In the opening scene, the number of the bus is 7734. According to John Waters, this is an old Catholic school joke since '7734' upside-down "spells" hell.
In a magazine interview done at the time of the film's release, Christina Ricci revealed that she hated Baltimore, John Waters's beloved home town and the main setting of this film. When he found out about this, Waters thought it was hilarious. Ricci also hated laundromats (her character is a workaholic laundromat manager) because she often had go to them as a child.
Pecker's camera is an early model of the Canonet, a compact camera made over a period of more than a decade (primarily in the 1960s) by Canon for the consumer market. The camera takes so-so pictures, and today might be worth $20-$40, when it can be found. It is entirely plausible that Pecker might find such a camera in a thrift store, at a garage sale, or the like.
The claw machine in the bar contains, among other things, a box of Ex-Lax, a box of Gas-X, a liquor bottle filled with a dark brown liquid (bourbon maybe?), and a cell phone.
At the meal after Pecker's New York exhibition opening, Pecker's gallerist Rorey Wheeler says "hi Colin, hi Pat" to characters off-screen. She is probably referencing Colin de Land and his wife Pat Hearn, both legendary New York gallery owners (of American Fine Arts, Co. and Pat Hearn Gallery respectively). At the time Pecker was filmed, director John Waters was represented by American Fine Arts, Co.
John Waters: As the voice of the pervert sexually harassing Shelley, played by Christina Ricci, over the phone.