Free Stamps With Candy Purchase In The The Late 1920-S-30-S

My mother just told me a story about my great-grandfather who was an avid stamp collector and an APS member who lived in Puerto Rico. When my grandmother was a little girl, he would occasionally call her from his office to tell her that the latest edition of a certain candy was now available. Included in the candy was a packet of stamps. My mother couldn't recall the brand of candy or what kind it was. She just remembers my grandmother saying how excited he was about this promotion and how much they both looked forward to it. Has anyone heard of something like this? It would have been in the late 1920s - early 30s. (He died in 1932.)

Thank you!
Aimee

The closest thing I can think of was a pack of trading cards like item called "World of Stamps" that came with a big slab of gum and a small packet of stamps. This would have been in the 1960's though.