Isn't this a neat concept!? The green container can hold formula until you are ready to prepare bottle or even a pacifier case. The top connects to the bottom so you don't lose it. Very clever. If only I could find a faster nipple. A one and a two are too slow and he gets frustrated/bored. It would be a nice way to organize his stuff for the sitter though (already have water measured in bottle and correct amount of formula in container connected to right bottle)