I've got a load of Cigarette Cards that my mothers cousin gave me (so 30s vintage I suppose).
Then a load more that I collected from Lyons tea in the 50s. You could send for a book to stick them in with all the information that was on the sticky side of the card reprinted round the space for that card.
And I made the model village from the back of the Rinso (soap powder) boxes. We got a lot of duplicates, I'm not sure if we ever completed the set.

To get the plastic model you had to eat the whole box of Corn Flakes, it was at the bottom. We were shocked to hear that some children OPENED THE BOX AT THE WRONG END.