If you ever need to display "full" milk bottles, here's a trick I learned.
You wash out a milk bottle and after it dries, you fill it up to the bottom of the neck with ordinary white flour. Pour it in a little at a time and tamp it down with a round dowel as you go. Pack it nice and tight. When you have reached the neck, stop. Then, to make it look like the cream has risen to the top of the milk, you fill the bottle the rest of the way with yellow cake mix, tamping it down as you go until it's all the way to the bottom of the rim. Then put in a cardboard bottle cap (available as reproductions), and you're done. It has the look and weight of a real quart of milk. It won't spoil, turn colors or anything.
If you need to create "chocolate milk", just substitute packaged brownie mix for the white flour.
I learned this from a fellow who had a restored DIVCO milk delivery truck on display at a car show. He had several wooden milk crates in the back with incredibly realistic bottles of milk. So I asked him how he did it, because it looked so much better than the tiny white foam plastic pellets you usually see. He said his wife actually came up with the idea. I went home, tried it, and it looks terrific. Try it.
