While growing up in the fifties and sixties you could just about get everything a kid needed fairly cheaply by mailing off a nominal sum of money and one or two specialy marked box tops of a product. Generally it was breakfast cereal that did this.
The custom of mailing off box tops was so prevalant that the Rocky and Bullwinkle show did a parody on it mentioning treating box tops like they were a form of currency, which in a way they were. All the money in the world would not buy a kid a baking soda submarine. You had to have the specially marked box top or you were just plain out of luck.
Of course, it was an advertising gimmick to get kids to get their mothrs to buy their cereal and to a certain extent it worked, and maybe better than I think.
When the kid across the street got a baking powder powered submarine, I got my mom to buy a box of the cereal so I could get one, too. They were pretty neat. You'd pull the conning tower off and put baking powder into a little compartment and put the thing in the tub and watch it submerge and surface a couple of times.
Of course, there were a lot of other neat little toys the cereal companies would advertise, but the submarine was the one I remember most.
Box tops were eventually replaced by those UPC bar codes a number of years back, but the idea is and was the same thing. You'd cut the UPC code off the box and send them in with your nominal sum.
Still, I'd bet that if I had been the one to empty my mothers home when she went to a retirement village, I'd have found a stash of box tops somewhere waiting for the cereal company to come up with some kind of toy I wanted.
As for the baking powder submarines?
They still make them and I saw one for sale for $3.59 on Amazon.
I might check it out because even though I am an old man, I am not too old to take a few minutes out to enjoy playing with a baking powder submarine in the bathtub.
What's pretty neat about it is that I don't have to pay for it in box tops.
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