Peddler's Wagon was a common type of vendor during the boom. This was a hold-over from years past when the peddler would go from door to door. During the boom, he would set up shop on a busy street, then travel to area farms on a regular schedule.
If the Arp General Store was the Wal-Mart of the 1930s, the peddler's wagon was the Amazon(dot)com of the period. He would take your order, and then deliver it the next time he made his rounds to your farm, probably in 30 days, unlike Amazon Prime 2 day delivery.
Look at the prices of the items on the wagon. There have been some price increases since 1930.