what are the “shopping trips”?

From the text:

Finally, by their cutting remarks, the family did exert enough pressure so that Grandmama and I no longer openly announced our expeditions. Instead, she took me with her on “shopping trips,” ostensibly for clothes or groceries, while in fact we spent most of our time exploring stranger and more distant neighborhoods, searching for splendid junk: jangling pieces of a vase, cranberry glass fragments embossed with leaves, discarded glass beads from Woolworth necklaces ….