The glass ones were made as give-aways back in the late 40's and by Chattanooga Glass Co...(Beware of Taiwan repos though.) They were filled and capped. I dug one in my dump last month. Not worth much but a "keeper."
The plastic ones were part of a toy set...a plastic case & 24 mini bottles...They also came with a toy truck but those were even smaller. Later, some plastic ones were issued with a small cardboard carton.
Up here in Canada you could get little glass ones made by the Dominion Glass Co. They were givin away when you bought a case of 6, or so I have heard. I have dug a few broken ones, and a couple whole ones. If they are in mint condition, they are worth about 10 bucks.
Here's a little plastic coke bottle that isn't. I do have a clear glass mini coke and a very pale aqua mini coke that has a C inside an O on the base (Owens Corning) I guess.