All day long, street vendors go by our house on the hem (lane off the main street). They sing out in patterns that one learns quickly so that you can step out of the house when you hear them coming to prepare to buy a snack or ingredient for dinner.
In this case, the woman with the pans suspended from a pole (carried on her shoulder) is selling bánh bèo, flat rice pastries in three varieties -- flat square pads with shredded pork and mung bean paste on top, fatter, doughy squares with mung bean paste inside, and flat jelly-like pads with red shrimp paste inside. All are soaked with nuoc mam (fish sauce), and taste great -- one of my favorites.
The woman's pans are like a prep. kitchen -- they contain everything needed to assemble these items on the spot.