remember when people used to mail loose coconuts from their Hawaii vacation just like a postcard?

The post office once charged only based on weight. I have many copper postcards as well as wooden ones. I even have a can of Florida Sunshine that was mailed to me in the 1980s as the actual mailpiece - not in a box. They might have been bumped up to a letter rate instead of the cheaper postcard rate, but if it was ounce or less it was one stamp. (the can was around 3 stamps, as I recall)

Mechanization changed all that and brought weight & dimension rates